Both could be signs there are leaks in the well that's been capped off for three days.
The official spoke to The Associated Press on condition of anonymity Sunday because an announcement about the next steps had not yet been made.
The official is familiar with the spill oversight but would not clarify what is seeping near the well. The official said BP is not complying with the government's demand for more monitoring. BP spokesman Mark Salt declined to comment on the allegation, but said "we continue to work very closely with all government scientists on this."
Retired Coast Guard Adm. Thad Allen will make the final decisions on the next step. The official said Allen would issue a letter to BP shortly allowing testing to proceed in 24-hour increments, but also requiring more analysis of the seep and the possible observation of methane over the well.
If Allen doesn't get the response he wants, the testing could stop, the official said.
The custom-built cap that finally cut off the oil flowing from BP's broken well three days ago was holding steady Sunday.
A BP official said the company hoped to leave the cap in place until crews can permanently kill the leak.
That differs from the plan the federal government laid out a day earlier, in which millions more gallons of oil could be released before the cap is connected to tankers at the surface and oil is sent to be collected through a mile of pipes.
Federal officials wary of making the well unstable have said that plan would relieve pressure on the cap and may be the safer option, but it would mean three days of oil flowing into the Gulf before the collection begins.