ARCO <ARC> RAISES CRUDE OIL POSTINGS 50 CTS Atlantic Richfield's Arco Oil and Gas Co said it increased contract prices for crude oil by 50 cts a barrel, effective today. Arco said the 50 cts increase brings its posted price for West Texas Intermediate, the U.S. benchmark grade, to 19.00 dlrs a barrel. The price of West Texas Sour was increased to 18.10 dlrs. Light Louisiana Sweet was raised to 19.35 dlrs. The price was last changed on September 30.