Insurance rates were increased 50% for cargoes in the Persian Gulf by London underwriters following the Iranian missile attack on Kuwait's offshore supertanker terminal. The War Risks Rating Committee has ruled that the premiums should go up to 0.75% of the value of a cargo from 0.50% for cargoes moving to and from ports in Kuwait and northern Saudi Arabia. The committee acts for member companies of the Institute of London Underwriters and for marine underwriters in the Lloyd's of London insurance market. The new rate is effective today. Prices rose on world markets. On the New York Mercantile Exchange, West Texas Intermediate--the benchmark U.S. crude--climbed 15 cents to $20.20 a barrel.