Published: May 18, 2010 2:17 PM EDT

TAMPA, Fla.  - University scientists are forecasting that oil from the spill off Louisiana could reach Florida's Key West by Sunday.

University of South Florida researchers said Tuesday the southern arm of the massive spill has entered or is near the so-called loop current, which circulates in the Gulf and takes water south to the Florida Keys and the Gulf Stream.

The Gulf Stream could eventually take the oil up Florida's Atlantic coast. Twenty tar balls were found by the Coast Guard off Key West on Monday. They are being tested to see if they came from the Louisiana spill or elsewhere.

Tar balls can occur naturally or come from other sources such as ships. USF scientists use currents, wind forecasts and other elements to make their predictions.