Take away Exxon Mobil Corp., Chevron Corp. and ConocoPhillips, and profits at U.S. companies are the worst in at least a decade, Bloomberg reported.

Without the $70 billion that oil producers earned in the last two quarters, profits at companies in the Standard & Poor’s 500 Index declined 26 percent and 30.2 percent in those quarters, the biggest decreases for any quarter since Bloomberg started compiling data in 1998.

Energy companies accounted for almost half the income growth reported by S&P 500 companies in the first three months of 2008 as oil prices rose past $100 per barrel, the data show.

The results leave the S&P susceptible to declines as oil companies’ costs swell and production slips, according to Bank of America Corp., Charles Schwab Corp. and Allianz Global Investors. As the rest of the U.S. economy is struggling, the industry is getting less profit from a barrel of oil than at any time since 2005. Still, energy shares posted the S&P 500’s steepest gains in the past year, inflating their representation to 15 percent of the index.

Energy companies in the S&P 500 reported an average 25.9 percent gain in first-quarter profits, the biggest of the index’s 10 industry groups, data compiled by Bloomberg show. For the broader market, earnings declined by 18.3 percent, based on the 441 companies in the S&P 500 that already announced results.