My guess for what it's worth...
Blocked oil strainer at pick up in the sump.
If its been sitting for some time and the oil was crap before it was parked, it would surely had turned to sludge. Engine warms and off it goes in big blobs.
Kia's have the problem on a regular basis. (Change oil every 5k or else)
On the other side, if the oil was really crap when it was parked, then the engine is likely to be very tired indeed..

Adam