CALGARY — Alberta's energy regulator has blocked the sale of sour gas wells, pipelines and other facilities from an energy giant to a much smaller company over clean-up concerns.

In a decision released Thursday, the regulator says Calgary-based Pieridae Energy's attempted purchase of the southern Alberta assets from Shell Canada goes against the intent of environmental laws.

The issue was seen as a test case of the regulator's determination to avoid clean-up costs for energy facilities falling to the taxpayer.

In its written decision, the Alberta Energy Regulator said the deal would have split the liability for cleaning up the sites.

It says that responsibility should remain with Shell.

It also says the extent of contamination at the hundreds of facilities is unknown.