ST. PAUL — A Minnesota mandate that most diesel fuel sold in warm-weather months be a blend containing 10 percent biodiesel faces an uncertain future.

Minnesota currently requires a year-round 5 percent blend known as B5 for most diesel sales. The B10 mandate is to begin in July, and then rise to 20 percent by next year.

But there have been delays as state officials worked to ensure adequate supplies and set up regulatory protocols. Those delays might continue.

The state commerce department previously said it wasn’t sure it could conduct timely inspections of retail outlets and trucking facilities to make certain the new standard would be met. There also was concern that blending facilities in southwest Minnesota had inadequate capacity.

North Mankato Rep. Clark Johnson recently proposed a bill that would push the 20 percent requirement back another three years, to 2018. He argued that the state again needs more time to prepare.

Johnson’s bill didn’t pass through its House committees before a March 21 deadline, but he said he believed it could still pass this year.

Biodiesel, which is made mostly from soybean oil, is promoted as an environmentally friendly, renewable fuel that creates jobs and demand for crops.

But the trucking industry opposes the mandate, mainly because of cost concerns. While biodiesel is cheaper than petroleum-based diesel right now, industry officials say there’s no guarantee it will stay that way.