Shares of major integrated oil companies were moving lower Tuesday as four giants were downgraded by Oppenheimer Tuesday morning. Chevron ( CVX), BP ( BP), Exxon Mobil ( XOM) and ConocoPhillips ( COP) were lowered from outperform to perform. Chevron, which warned on its first-quarter results late Thursday, was recently trading down 2% to $66.62. BP was lower by 1.7% to $39.25. Exxon Mobil was off 1.6% to $66.93. ConocoPhillips was down 0.3% to $39.94. The Amex Oil Index was lower by 0.6%, to 880.82.Light, sweet crude oil futures for May delivery were recently hovering around $50 a barrel, down 23 cents to $49.82. Sunoco ( SUN) was trading at $28.07, down 1.4%. Royal Dutch Shell ( RDS-B) was down 1.7% to $41.67.