Futures are lower

Stock futures are slightly lower on this Friday morning.

Near 8:20 a.m. ET, Dow futures were down 39 points, S&P 500 futures were down 5 points, and Nasdaq futures were down 13 points.

Yesterday's session was quite choppy and the major indexes ended up nearly flat.

Oil prices sank even lower to a fresh six-year low. West Texas Intermediate crude oil futures fell to around $41.46 in New York. In a morning note, Societe Generale's Kit Juckes told clients that financial markets are beginning to understand that solving the problem of oversupply and weak demand needs "a more protracted undershoot in oil prices."

China's central bank set the yuan at 6.3974, below the 6.3990 level that it closed on Thursday. The currency stopped tumbling after three days of devaluation.

In economic data, the producer price index rose 0.1% in July, versus 0.2% expected. The gauge of future inflation rose for a third month.

We'll also get data on industrial production, and the University of Michigan's consumer sentiment index this morning.

Around 1:00 p.m. ET, Baker Hughes will release the latest count of US oil and gas rigs.