Why on earth is Cushing, Oklahoma so important to world energy markets? The answer: because it's home to a major oil depot that holds approximately 10% of the nation's non-Strategic stockpiles (about 32 out of 320 million barrels, depending on the season). See this article in the Wall Street Journal for more information: Where has all the oil gone?
Consequently, the price for West Texas Intermediate (WTI) light, sweet crude as delivered to Cushing has become one of the global oil price benchmarks. For example, indexes of energy prices often include "WTI Cushing Spot" as one of the standard listings. Here's the way it's listed at Bloomberg news: Bloomberg Energy Prices
Interestingly enough, the Wall Street Journal is reporting that Cushing's inventories are much lower than normal because today's spot prices are higher than the prices for future delivery.