April 21 (Bloomberg) -- ConocoPhillips, the third-largest U.S. oil producer, stopped production at its J-Block oil and gas fields in the U.K.'s North Sea on an ``operational problem.''

The fields were shut down about 5 p.m. London time yesterday, spokeswoman Sandra Ross said today in a telephone interview. The company is working to get the fields back online, she said, without providing more details.

To contact the reporter on this story: Paul Dobson in London at pdobson2@bloomberg.net

Last Updated: April 21, 2008 05:29 EDT