Oil prices fell slightly Friday in thin trading but still ended with a gain for the week, mainly because of OPEC's decision to trim production now that the gulf war is over, traders said.

Crude oil for April delivery on the New York Mercantile Exchange fell 26 cents Friday to close at $20.01 a barrel, an increase of 70 cents over last week's close.Prices rose early in the week after the Organization of Petroleum Exporting Countries said it would cut output to 22.3 million barrels per day from a current level of about 23 million barrels.

Prices later declined, and most traders said the OPEC cut was less than expected.

Oil prices should move cautiously higher next week as seasonal gasoline demand continues to support prices, but analysts expect price moves to be slight as the market seeks longer-term directon.