NEW YORK (TheStreet) -- With the price of crude oil falling by almost 60% since its high in 2014, we decided to check TheStreet Quant Ratings for oil companies that would be good investments. We narrowed the search down to large-cap oil refiners.

Oil dropped to just over $40 per barrel, and oil stocks have taken a hit. If you're worried that oil will stay at a low price, then refiners are a good investment.

They do very well when the price of crude is low. Low prices means they can refine more oil, so, apart from the initial hit on inventory, future profit opportunities are strong. People also tend to buy more gas when oil is low, so there's more demand for the refineries.

So, what are the best oil refiners investors should be buying? Here are the top four, according to TheStreet Ratings, TheStreet's proprietary ratings tool.

TheStreet Ratings projects a stock's total return potential over a 12-month period including both price appreciation and dividends. Based on 32 major data points, TheStreet Ratings uses a quantitative approach to rating over 4,300 stocks to predict return potential for the next year. The model is both objective, using elements such as volatility of past operating revenues, financial strength, and company cash flows, and subjective, including expected equities market returns, future interest rates, implied industry outlook and forecasted company earnings.

Buying an S&P 500 stock that TheStreet Ratings rated a buy yielded a 16.56% return in 2014, beating the S&P 500 Total Return Index by 304 basis points. Buying a Russell 2000 stock that TheStreet Ratings rated a buy yielded a 9.5% return in 2014, beating the Russell 2000 index, including dividends reinvested, by 460 basis points last year.

Check out which stocks made the list. And when you're done, be sure to read about which mid-cap energy stocks you should buy now. Year-to-date returns are based on August 21, 2015 closing prices. The highest-rated stock appears last.

MPC Chart MPC data by YCharts
4. Marathon Petroleum Corporation (MPC - Get Report)
Rating: Buy, A
Market Cap: $30 billion
Year-to-date return: %%%

Marathon Petroleum Corporation, together with its subsidiaries, engages in refining, marketing, retailing, and transporting petroleum products primarily in the United States. It operates through three segments: Refining & Marketing, Speedway, and Pipeline Transportation.

"We rate MARATHON PETROLEUM CORP (MPC) a BUY. This is based on the convergence of positive investment measures, which should help this stock outperform the majority of stocks that we rate. The company's strengths can be seen in multiple areas, such as its solid stock price performance, notable return on equity, attractive valuation levels, good cash flow from operations and growth in earnings per share. We feel its strengths outweigh the fact that the company shows low profit margins."

Highlights from the analysis by TheStreet Ratings Team goes as follows:

  • Investors have apparently begun to recognize positive factors similar to those we have mentioned in this report, including earnings growth. This has helped drive up the company's shares by a sharp 30.35% over the past year, a rise that has exceeded that of the S&P 500 Index. Regarding the stock's future course, although almost any stock can fall in a broad market decline, MPC should continue to move higher despite the fact that it has already enjoyed a very nice gain in the past year.
  • Current return on equity exceeded its ROE from the same quarter one year prior. This is a clear sign of strength within the company. When compared to other companies in the Oil, Gas & Consumable Fuels industry and the overall market, MARATHON PETROLEUM CORP's return on equity exceeds that of the industry average and significantly exceeds that of the S&P 500.
  • Net operating cash flow has increased to $994.00 million or 13.21% when compared to the same quarter last year. The firm also exceeded the industry average cash flow growth rate of -20.65%.
  • MARATHON PETROLEUM CORP's earnings per share improvement from the most recent quarter was slightly positive. The company has demonstrated a pattern of positive earnings per share growth over the past year. We feel that this trend should continue. During the past fiscal year, MARATHON PETROLEUM CORP increased its bottom line by earning $4.42 versus $3.31 in the prior year. This year, the market expects an improvement in earnings ($5.68 versus $4.42).

PSX Chart PSX data by YCharts

3. Phillips 66 (PSX - Get Report)
Rating: Buy, A
Market Cap: $45 billion
Year-to-date return: %%%

Phillips 66 operates as an energy manufacturing and logistics company. It operates through four segments: Midstream, Chemicals, Refining, and Marketing and Specialties (M&S).

"We rate PHILLIPS 66 (PSX) a BUY. This is based on the convergence of positive investment measures, which should help this stock outperform the majority of stocks that we rate. The company's strengths can be seen in multiple areas, such as its increase in net income, largely solid financial position with reasonable debt levels by most measures, attractive valuation levels, good cash flow from operations and notable return on equity. We feel its strengths outweigh the fact that the company shows low profit margins."

Highlights from the analysis by TheStreet Ratings Team goes as follows:

  • The net income growth from the same quarter one year ago has significantly exceeded that of the S&P 500 and the Oil, Gas & Consumable Fuels industry. The net income increased by 17.3% when compared to the same quarter one year prior, going from $863.00 million to $1,012.00 million.
  • The current debt-to-equity ratio, 0.40, is low and is below the industry average, implying that there has been successful management of debt levels. Along with the favorable debt-to-equity ratio, the company maintains an adequate quick ratio of 1.16, which illustrates the ability to avoid short-term cash problems.
  • Net operating cash flow has significantly increased by 71.92% to $1,427.00 million when compared to the same quarter last year. In addition, PHILLIPS 66 has also vastly surpassed the industry average cash flow growth rate of -20.65%.
  • Current return on equity exceeded its ROE from the same quarter one year prior. This is a clear sign of strength within the company. Compared to other companies in the Oil, Gas & Consumable Fuels industry and the overall market on the basis of return on equity, PHILLIPS 66 has underperformed in comparison with the industry average, but has exceeded that of the S&P 500.

TSO Chart TSO data by YCharts

2. Tesoro Corporation (TSO
Rating: Buy, A+
Market Cap: $13 billion
Year-to-date return: %%%

Tesoro Corporation, through its subsidiaries, engages in petroleum refining and marketing activities in the United States. It operates in three segments: Refining, Tesoro Logistics LP (TLLP), and Retail.

"We rate TESORO CORP (TSO) a BUY. This is based on the convergence of positive investment measures, which should help this stock outperform the majority of stocks that we rate. The company's strengths can be seen in multiple areas, such as its solid stock price performance, impressive record of earnings per share growth, compelling growth in net income, notable return on equity and attractive valuation levels. We feel its strengths outweigh the fact that the company has had generally high debt management risk by most measures that we evaluated."

Highlights from the analysis by TheStreet Ratings Team goes as follows:

  • Powered by its strong earnings growth of 171.76% and other important driving factors, this stock has surged by 64.60% over the past year, outperforming the rise in the S&P 500 Index during the same period. Regarding the stock's future course, although almost any stock can fall in a broad market decline, TSO should continue to move higher despite the fact that it has already enjoyed a very nice gain in the past year.
  • TESORO CORP reported significant earnings per share improvement in the most recent quarter compared to the same quarter a year ago. The company has demonstrated a pattern of positive earnings per share growth over the past two years. We feel that this trend should continue. During the past fiscal year, TESORO CORP increased its bottom line by earning $6.69 versus $2.83 in the prior year. This year, the market expects an improvement in earnings ($11.53 versus $6.69).
  • The net income growth from the same quarter one year ago has significantly exceeded that of the S&P 500 and the Oil, Gas & Consumable Fuels industry. The net income increased by 159.8% when compared to the same quarter one year prior, rising from $224.00 million to $582.00 million.
  • The company's current return on equity greatly increased when compared to its ROE from the same quarter one year prior. This is a signal of significant strength within the corporation. When compared to other companies in the Oil, Gas & Consumable Fuels industry and the overall market, TESORO CORP's return on equity exceeds that of the industry average and significantly exceeds that of the S&P 500.

VLO Chart VLO data by YCharts
1. Valero Energy Corporation (VLO - Get Report)
Rating: Buy, A+
Market Cap: $13 billion
Year-to-date return: %%%

Valero Energy Corporation operates as an independent petroleum refining and marketing company in the United States, Canada, the Caribbean, the United Kingdom, and Ireland. It operates through two segments, Refining and Ethanol.

"We rate VALERO ENERGY CORP (VLO) a BUY. This is based on the convergence of positive investment measures, which should help this stock outperform the majority of stocks that we rate. The company's strengths can be seen in multiple areas, such as its solid stock price performance, impressive record of earnings per share growth, compelling growth in net income, largely solid financial position with reasonable debt levels by most measures and notable return on equity. We feel its strengths outweigh the fact that the company shows low profit margins."

Highlights from the analysis by TheStreet Ratings Team goes as follows:

  • Powered by its strong earnings growth of 118.03% and other important driving factors, this stock has surged by 35.74% over the past year, outperforming the rise in the S&P 500 Index during the same period. Regarding the stock's future course, although almost any stock can fall in a broad market decline, VLO should continue to move higher despite the fact that it has already enjoyed a very nice gain in the past year.
  • VALERO ENERGY CORP reported significant earnings per share improvement in the most recent quarter compared to the same quarter a year ago. The company has demonstrated a pattern of positive earnings per share growth over the past two years. We feel that this trend should continue. During the past fiscal year, VALERO ENERGY CORP increased its bottom line by earning $6.98 versus $4.97 in the prior year. This year, the market expects an improvement in earnings ($8.02 versus $6.98).
  • The net income growth from the same quarter one year ago has significantly exceeded that of the S&P 500 and the Oil, Gas & Consumable Fuels industry. The net income increased by 129.8% when compared to the same quarter one year prior, rising from $588.00 million to $1,351.00 million.
  • The current debt-to-equity ratio, 0.34, is low and is below the industry average, implying that there has been successful management of debt levels. Along with the favorable debt-to-equity ratio, the company maintains an adequate quick ratio of 1.17, which illustrates the ability to avoid short-term cash problems.
  • Current return on equity exceeded its ROE from the same quarter one year prior. This is a clear sign of strength within the company. Compared to other companies in the Oil, Gas & Consumable Fuels industry and the overall market, VALERO ENERGY CORP's return on equity exceeds that of both the industry average and the S&P 500.

Must Read: