If the war is loser to OTL with a German led victory then I think this Bulgaria gets most of the territory desired and set forth by others, Bulgaria becomes a major power and lynch pin in the CP's alliance, dominating the Balkans and not just linking to the OE but in subtle ways counterbalancing it. Romania and Serbia both are under its heel in partnership with the Germans in Romania and A-H in Serbia. Bulgaria will hold Greece to a future of strict neutrality with decidedly pro-German leaning as desired. Bulgaria likely sees a boosted naval component to maintain CP authority in the Black Sea and Aegean, it becomes a cross roads to the OE. As one pairs back the CP "victory" towards a more modest stalemate and status quo end to the war Bulgaria may not get aggrandized as much but would remain an important piece of the CP puzzle. At minimum I think it folds in the German dominated customs union, this links the Balkans to the bigger continental economy, it should bring industry and growth to Bulgaria, a country that will become a serious lesser power in Europe, the near-East and Eastern Mediterranean.
As to OE oil, the Mesopotamian fields were suspected to be substantial, this will draw the Germans in to invest and develop, as I assume the British lose out and surrender their position in the OE. We might speculate that this oil gets online earlier than the late-1930s and by the 1940s is producing more like modern volumes as Germany needs a secure supply. Thus the impact is not immediate but substantial to a long term outlook for the CPs who will be exhausting Galicia in short order, draining Romania and otherwise beholden to buy American or Russian with only the Dutch being a relatively secure exporting source. Now after the 1960s is when the potential for Arabian oil and I think most importantly its gas becomes game changing. A surviving OE can pipe the Gulf gas to Europe, something that would greatly alter the economics of energy and transportation, alter environmental issues and otherwise impact Europe's energy infrastructure. Rather than diesel we see LNG, less or no nuclear, the phase down of coal and phase out of lignite, no Russian monopoly on gas or oil exports, and so on. The effect is more than money into the OE.