Because of the fundamentals of gas, secondary market for oil is more developed than that for gas which still relies more on long term contracts.

The secondary market is essentially the oil trading market. The same cargo or parcel of oil can change hands many times before it is actually loaded on a tanker or delivered. It’s also the basis of the oil derivatives market and enables producers, suppliers and traders to hedge their positions or take long or short positions into the future depending on what they think is the future direction of oil prices. The fact that there is more of a secondary market in oil then gas reflects one of the fundamental differences between the two products.

Oil can more or less be shipped anywhere in the world that a tanker can unload; gas tends to have fixed supply chains determined by pipeline connections or LNG chains. So, secondary markets in gas tend only to be located at hubs where multiple pipelines can deliver/offtake gas e.g. Henry Hub in USA or Zeebrugge in Belgium.