The party to an oil & gas lease that is granted the rights to explore for, drill, and produce hydrocarbons in the subsurface of a leased tract. The lessee must bear all the costs and expenses of the operations, but if successful, it is entitled to the production net of royalties owed to the grantor. The property interest held by the lessee is a fee simple determinable and commonly known as leasehold interest, working interest, or operating interest. The lessee usually is an upstream oil & gas company.