Though now more-commonly discussed as something that wars are fought over, it isn't widely known outside historians just how big a role the need for oil played WW2.
In order to facilitate the rapid expansion of the Nazi empire across Europe, Hitler and co would need an almost ungodly amount of oil. Without a sufficient supply, the armoured divisions that had rolled both east and westward with such unprecedented success would be ground to an almost immediate halt, with Germany just not having the natural resources to remedy this.
With that in mind, Hitler knew he needed to source a supply of liquid gold right from the early stages of the war. Even while the German-Soviet pseudo-truce was ongoing and the two powers had agreed to carve up Poland between them in the 1939 'friendship' pact, Hitler was well aware of the acute oil shortages his regime faced, and how unlikely it was that a war on the scale of WW2 could be maintained without capturing a massive source of oil.
This is the primary reason that Hitler chose to invade the Soviet Union when he did. British naval blockades had starved the axis power of one of the war's most pivotal resources, and if the invasion of the USSR had been delayed any longer, Nazi Germany simply wouldn't have had the resources required to make the necessary advances.
This is also the reason Hitler was so fixated on capturing Stalingrad. Of course, it would've been nice for him to get one over on his fellow dictator by capturing a city named after the Soviet supreme, but it was what laid beyond the city, the oil-rich Caucasus area that was the true prize in the eyes of the Führer.
By failing to succeed in having Operation Barbarossa be the quick and fatal blow against the USSR as it was intended, the war had already turned decisively against Germany and though the regime could continue to wage war following that point, the opportunity to emerge with any kind of victory was all but lost from the defeat at Stalingrad onwards.