why would car run a half hour then stall on 1991 Buick Skylark

runs fine awhile then it just stalls have to let it set about 15 minutes then it will run fine for a few then stall again

number #1 is correct, does the vehicle fire back up immeditly or do you have to let cool
2 more answers
My guess is a defective crankshaft sensor.
Im having same problem. Research is telling me its either crankshaft or head gasket. Let me know which one you do/did and if it worked