Narrative:

Departing ZZZ following a type-specific inspection activity. While in climb out; oil was seen on the windscreen. An emergency was declared with immediate return to the airport. A safe landing was accomplished in spite of the interference with visibility. The oil filler cap was apparently not tightly replaced as it was found loose in the engine compartment. There was a loss of approximately 1 quart of oil. On-field fire department personnel responded timely; but were not needed.

Google
 

Original NASA ASRS Text

Title: A BE33 PILOT EXPERIENCED OIL ON HIS WINDSCREEN AFTER TAKEOFF. HE DECLARED AN EMERGENCY AND RETURNED TO LAND; WHERE HE FOUND THE OIL FILLER CAP LOOSE.

Narrative: DEPARTING ZZZ FOLLOWING A TYPE-SPECIFIC INSPECTION ACTIVITY. WHILE IN CLBOUT; OIL WAS SEEN ON THE WINDSCREEN. AN EMER WAS DECLARED WITH IMMEDIATE RETURN TO THE ARPT. A SAFE LNDG WAS ACCOMPLISHED IN SPITE OF THE INTERFERENCE WITH VISIBILITY. THE OIL FILLER CAP WAS APPARENTLY NOT TIGHTLY REPLACED AS IT WAS FOUND LOOSE IN THE ENG COMPARTMENT. THERE WAS A LOSS OF APPROX 1 QUART OF OIL. ON-FIELD FIRE DEPT PERSONNEL RESPONDED TIMELY; BUT WERE NOT NEEDED.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.