Shares of oil companies were trading lower in the last half hour of trading on Monday as crude oil futures and the stock market moved down.

Light, sweet crude futures for May delivery settled down $4.52 to $45.81 on the New York Mercantile Exchange.

The Amex Oil Index was down 4.8% to $41.58.

Shares of Exxon Mobil ( XOM), which moved up a spot to No. 1 on this year's Fortune 500 list, were down 2.1% to $65.34.

Fortune's closely watched list, released Sunday, ranked companies by their revenue in 2008. Exxon had revenue of $442.85 billion last year, up almost 19% from 2007. The Irving, Texas-based company also made the biggest annual profit at $45.2 billion. Exxon also announced Monday that it and its employees donated more than $36 million to 900 U.S. colleges and universities in 2008.

Chevron ( CVX), No. 3 on the Fortune 500, was down 2.9% to $64.07.

Also for Chevron, Fitch Ratings affirmed an investment-grade rating for the issuer default rating and senior unsecured notes, citing the company's integrated oil business model, the size and quality of its worldwide asset base, its strong cash flow generation capability, conservative financial management and low debt levels.

"Chevron's 2008 credit metrics were very strong, driven by outperformance at the company's upstream (exploration and production) arm and lower debt balances of recent years," Fitch analyst Mark Sadeghian wrote Friday.

ConocoPhillips ( COP), fourth on the Fortune 500, was down 5.4% to $37.99.

(The good publicity for the three Dow Jones Industrial Average components wasn't helping that average Monday, however.)

BP ( BP) was down 3.1% to $38.87.

Sunoco ( SUN) was down 5.8% to $26.51.

Royal Dutch Shell ( RDS.B) was off 2% to $41.20.
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