Energy futures ended higher Friday led by strength in gasoline, after a choppy week of trading sparked by concern about seasonal demand weakness. On the New York Mercantile Exchange, the May contract for West Texas Intermediate, the key grade of U.S. crude oil, rose 39 cents to finish at $20.39 a 42-gallon barrel after a 4-cent rise on Thursday. Contracts for later delivery also advanced. Among refined products traded on the exchange, wholesale unleaded gasoline for delivery next month, which fell 0.56 cent in the previous session, advanced 0.28 cent to 57.66 cents a gallon. May unleaded gasoline jumped 1.56 cents to 63.54 cents and June gained 0.98 cent to 62.77 cents. No. 2 heating oil for April delivery ended at 55.46 cents a gallon, up 0.45 cent, while May gained 0.70 cent to 53.67 cents and June rose 0.89 cent to 52.98 cents. Analysts said two consecutive weeks of lower gasoline inventories was bullish for the gasoline market and helped buoy the crude and heating oil markets. Tighter gasoline supplies around the Gulf of Mexico became more noticeable late Thursday, they said. ``Demand for gasoline is picking up in the Gulf. Apparently there's not as much available as people thought so gasoline led the market up,'' said Tom Bentz, director of futures trades for United Energy Inc. Analysts attributed the lower gasoline supplies partly to seasonal refinery maintenance, when big oil companies close refineries for annual repair. During the maintenance period, refineries use less crude oil and make fewer fuel products, such as gasoline. Oil prices have sagged in recent weeks due mainly to increasing supplies and slowing demand. OPEC is believed to be producing about 1 million barrels a day more of crude oil than the market can absorb.