What was found
RETURNED TO PHL, ACFT WAS GNDED. DURING TAKEOFF A STRONG ODOR OF OIL, MUSTY DIRTY SOCKS BEGAN, IT CONTINUED FOR SEVERAL MINUTES. THEN SUBSIDED. ODOR WAS STRONGER TOWARD THE FRONT OF THE ACFT. THE FLIGHT CREW DECLARED AN EMER & RETURNED WHERE THE ACFT LANDED SAFELY. AFTER LANDING THE FLIGHT ATTENDANT REPORTED THE ODOR AGAIN. ACCOMPLISHED AIR QUALITY TROUBLESHOOTING TASK CARDS, JC 43L000722001, 43L00021001, & 43L00036002. GND RAN BOTH ENGS & APU TO HIGH POWER & ALL CHECKS WERE NORMAL. IT WAS NOTED THAT DURING THE PREVIOUS RON, BOTH ENGS HAD A COMPRESSOR WAS ACCOMPLISHED.