Take note that sweet and sour crude does not necessarily refer to the taste of crude oil but rather their formulation that can make crude oil either sweet or sour. Crude oil is known to be unrefined oil that comes with a lot of sulfur. It is the sulfur content that can determine if the oil is going to be sweet or sour. Sour crude oil means that it has a lot of sulfur while sweet crude oil means that it has lesser sulfur content.
Do remember that crude oil that comes with lower sulfur content is considered to be better to the environment as compared to those with high sulfur content. The more pollutants that are available in oil, the more that the environment will get affected.