A containment system having a containment dome and a seal plate which is attached to an oil wellhead casing or riser to prevent oil spills and contamination when an oil leak occurs. The containment dome is sealed to the seal plate by a compression mechanism so that oil will not leak from the containment dome. The containment dome can provide a wellhead patch to a wellhead system wherein the wellhead patch can interface with a capping stack. Chemicals can be injected into the containment dome to prevent hydrates from forming. All aspects of controlling and operating an oil wellhead can be performed through the containment dome and seal plate, and all aspects of installation, regulation, and control of the containment dome can be performed by remote operating vehicles under water.