A relentless upward march in oil prices and a bounce in real estate elevated two exchange-traded funds onto TheStreet.com Ratings list of the 20 most popular exchange-traded funds for April.

The accompanying table of the 20 ETFs with the largest average daily dollar volume of trading for the month includes the

United States Oil Fund

(USO) - Get Report

and the

iShares Dow Jones U.S. Real Estate ETF

(IYR) - Get Report

, each of which ranked outside the top 20 a month earlier.

They were joined as new members by the

SPDR Mid Cap 400

(MDY) - Get Report

. The MDY ETF becomes the only mid-cap fund in the top 20.

The five-highest dollar turnover funds remained in the same sequence as in the previous month, led by the granddaddy of all ETFs, the "Spider"

SPDR S&P 500 ETF

(SPY) - Get Report

, with $24.68 billion in average daily trading volume for the month.

Even though the popular stock market indices enjoyed bounces in the 4% to 6% range during April, four ProShares "Ultra Short" leveraged inverse funds remained on the list of the 20 most popular ETFs. But while the

ProShares Ultra Short QQQ

(QID) - Get Report

, which moves inversely at double the amplitude of the Nasdaq 100 index, slipped from sixth to ninth position, the "real deal"

PowerShares QQQ

(QQQQ)

, commonly referred to as the "Cubes," remained in second place on the array.

Similarly, the

ProShares Ultra Short Financials

(SKF) - Get Report

skidded from 10th spot to 13th on the list while a "long" financial ETF, the

Financial Select Sector SPDR

(XLE) - Get Report

, held steady in the fourth spot.

The index of the 100 biggest Nasdaq-listed funds proved to be the most popular market gauge among the most ETFs on the list. Joining the QQQQ and the QID in using the index, the leveraged

ProShares Ultra QQQ

(QLD) - Get Report

moved from 17th a month earlier to 16th at the end of April.

As for ETFs that were in the top 20 a month earlier and fell off the list in April, the weakening economy and its dampening impact on consumer sentiment resulted in

HOLDRs Retail

(RTH) - Get Report

dropping out of the table. The other dropouts from March were the

Materials Select Sector SPDR

(XLB) - Get Report

and the

iShares MSCI Japan

(EWJ) - Get Report

.

As for sectors, the aforementioned U.S. Oil Fund was joined by the

Energy Select SPDR

(XLF) - Get Report

and

HOLDRs Oil Services

(OIH) - Get Report

to provide choices in the energy realm.

Emerging markets -- specifically, the popular BRIC (Brazil, Russia, India and China) funds -- are represented in the table by the

iShares MSCI Emerging Markets ETF

(EEM) - Get Report

in the fifth spot, by number 13 in

iShares FTSE/Xinhua China 25

(FXI) - Get Report

and in the 15th spot the

iShares UMSI Brazil ETF

(EWZ) - Get Report

.

Twelve of the 20 favorite ETFs outperformed the SPDR S&P 500, which mimics "the market," while seven underperformed the popular benchmark. Six of the ETFs achieved double-digit gains for the month, while five ended with negative returns for the month.

Two of the members of the table sport the highest possible grades of A+ from TheStreet.com Ratings; seven have marks in the "B" range as "buy" recommended. Eight ended with grades in the "C" range, which equate with "hold" recommendations. Two ETFs with grades in the "D" range and one with the lowest possible mark of E- are tagged as "sell" recommendations.

The estimated average daily dollar volume figures for the month are computed by multiplying each fund's average daily share turnover by the geometric average of the fund's March and April closing prices.

Richard Widows is a senior financial analyst for TheStreet.com Ratings. Prior to joining TheStreet.com, Widows was senior product manager for quantitative analytics at Thomson Financial. After receiving an M.B.A. from Santa Clara University in California, his career included development of investment information systems at data firms, including the Lipper division of Reuters. His international experience includes assignments in the U.K. and East Asia.