It was not immediately clear why both Syria and the U.S. would claim a similar operation in the Omar oil field. The U.S. has said it is not cooperating with President Bashar Assad's government in the battle against the Islamic State group. But it has always said it gives the Syrian government a heads up on operations within its borders.
http://www.wxyz.com/news/world/us-commandos-kill-senior-isis-commander-in-syria-raid
Here is another article on the killing of Sayyef, who apparently was getting big bucks for ISIL selling captured oil. In addition to ISIL being more accurate than ISIS, as well as not insulting a nice little goddess, you should be aware that some anti ISIL Muslims call then Daesh, which I read has an insulting slang relationship to feet. Remember when President Bush was severely insulted by having a shoe thrown at him?
http://www.aol.com/article/2015/05/16/us-commandos-kill-senior-is-commander-in-syria-raid/21184097/