Firefighters have warned children not to play with matches following a blaze which destroyed 20 tonnes of straw.
They spent five hours dealing with the straw in a small barn at Astley Bridge Farm, Merton Road, near Ambrosden.
Leading firefighter Bob Swanton said: "We are pretty sure it was youngsters who started it, the farmer told us he saw kids on the land earlier.
"The barn had an asbestos roof which caused us a few problems."
The blaze started at 6pm and two fire engines from Bicester attended.
Mr Swanton added: "The message is that children shouldn't play with matches around bales of hay or straw.
"They think fires won't develop into something fairly large, but they do and they can be very dangerous."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article