Sept. 2, 1998 Ultramar Diamond Shamrock Corp. and a division and 2 subsidiaries of Koch Industries finalised the creation of a joint venture that combines the companies' natural gas liquids and petrochemicals operations in Mont Belvieu, Texas.
The new business, to be called Diamond-Koch and headquartered in Houston, Texas, will offer customers a more efficient source for transportation, storage, processing and distribution needs for both natural gas and refinery liquids and petrochemical feedstocks.
Diamond-Koch's assets include:

- UDS' majority interest in Mont Belvieu propylene splitters and related distribution pipelines and terminals
- UDS' Mont Belvieu hydrocarbon storage operation
- Koch Hydrocarbon's majority interest in the Mont Belvieu I natural gas liquids fractionator
- Certain UDS and Koch Pipeline Company supply systems