The credit ratings of three oil firms were flagged.

Standard & Poor’s said the sharp decline in oil prices prompted it to pay special attention to the financial condition of Arco, Chevron and Mobil as a prelude to possibly downgrading their credit ratings. In each case, any changes in ratings are expected to be minor, the credit rating firm said. Also placed on its “Creditwatch” list was Union Texas Petroleum Holdings. Standard & Poor’s took similar action on several other oil producers in February, when oil prices began their dramatic fall.