Priceline already operates Rentalcars.com, which it bought in 2003. Rental cars are the second biggest part of Priceline after its bread-and-butter hotel-bookings business.  

Investors will have to pay for Priceline's growth. Shares are trading at 32 times trailing earnings, compared with 19.6 for the S&P 500 Index.

The stock closed Tuesday at $1,246.77, up $43.77, or 3.6%. During the last decade, it has soared almost 50 times from about $25 a share, The Nasdaq Composite index has just more than doubled during that period.

But by some measures, the stock is reasonably priced. It trades at 19 times the company's expected earnings for 2015, and its PEG ratio (price-to-earnings ratio divided by the expected earnings growth rate) is 1.18, not a particularly high number.

So investors may want to consider whether Priceline's growth -- boosted by its car-rental business -- makes the company's stock still compelling at current levels. 

At the time of publication, the author held no positions in any of the stocks mentioned.

This article represents the opinion of a contributor and not necessarily that of TheStreet or its editorial staff.

TheStreet Ratings team rates PRICELINE GROUP INC as a Buy with a ratings score of B+. TheStreet Ratings Team has this to say about their recommendation:

"We rate PRICELINE GROUP INC (PCLN) a BUY. This is driven by some important positives, which we believe should have a greater impact than any weaknesses, and should give investors a better performance opportunity than most stocks we cover. The company's strengths can be seen in multiple areas, such as its robust revenue growth, largely solid financial position with reasonable debt levels by most measures, solid stock price performance, impressive record of earnings per share growth and expanding profit margins. We feel these strengths outweigh the fact that the company shows weak operating cash flow."

Highlights from the analysis by TheStreet Ratings Team goes as follows:
  • The revenue growth came in higher than the industry average of 4.3%. Since the same quarter one year prior, revenues rose by 26.1%. Growth in the company's revenue appears to have helped boost the earnings per share.
  • Although PCLN's debt-to-equity ratio of 0.26 is very low, it is currently higher than that of the industry average. Along with this, the company maintains a quick ratio of 5.14, which clearly demonstrates the ability to cover short-term cash needs.
  • Powered by its strong earnings growth of 31.30% and other important driving factors, this stock has surged by 48.57% 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, PCLN should continue to move higher despite the fact that it has already enjoyed a very nice gain in the past year.
  • PRICELINE GROUP INC has improved earnings per share by 31.3% 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, PRICELINE GROUP INC increased its bottom line by earning $36.01 versus $27.71 in the prior year. This year, the market expects an improvement in earnings ($52.31 versus $36.01).
  • The gross profit margin for PRICELINE GROUP INC is currently very high, coming in at 85.67%. It has increased from the same quarter the previous year. Along with this, the net profit margin of 20.17% significantly outperformed against the industry average.

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