B737-800 Captain reported experiencing an apparent fuel leak in the left tank during climb. Flight returned safely to departure airport.

Narrative

Climbing through 30;000 ft I noticed a fuel imbalance of approximately 1200 lbs. The left tank was the low tank. I immediately started cross feeding and asked ATC to level off sooner than cruise altitude. We cross fed for a couple of minutes and the left tank continued to decrease. After losing approximately two hundred pounds more fuel; we [requested priority handling] and turned back towards ZZZ [airport]. We were approximately 150 miles from the field. I assigned the FO pilot flying duties and comms. I ran the precautionary landing checklist. The left tank continued to drain the whole way in. We were cross feeding until final approach. After landing; we stopped on the runway; shutdown the left engine; and CFR (Crash Fire Rescue) inspected the aircraft. No fuel was seen leaking so we taxied to the gateCause: I had this exact same scenario happen to me several months prior. In that event; I ran the engine fuel leak QRH procedure which did not help. It leads to an engine shutdown which I did not think was prudent. I felt I was in the exact same position this time. I felt it was best to turn back towards ZZZ and land.