A shortage of oil limited Italian naval operations but the accumulation of ships at Alexandria and decrypted wireless messages from Colonel Bonner Fellers, the US Military attaché in Cairo (, the good source), alerted the  that convoys were about to be run from Alexandria and Gibraltar to Malta.
The limited availability of oil impacted Italian naval capabilities, but intelligence gathered from the concentration of ships in Alexandria and intercepted communications from Colonel Bonner Fellers, a trustworthy source, revealed plans for convoys departing from Alexandria and Gibraltar to Malta.