Oil companies are required to comply with discriminatory local content requirements with regards to service agencies. Coal mining companies are equally required to meet local content requirements [see entry on Mining - except energy producing materials].
Preference for Zambian products , etc. 
63. (1) A holder of a licence issued under this Act, shall, in the conduct of petroleum operations under the licence, and in the purchase, construction and installation of facilities, give preference to the maximum extent possible consistent with safety, efficiency and economy, to— (a) materials and products made in Zambia; and (b) service agencies located in Zambia and owned by Zambian citizens or bodies corporate registered under the Companies Act. [...]" (THE PETROLEUM (EXPLORATION AND PRODUCTION) ACT, 2008
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[For coal regulations: please see entry on Mining & Quarrying – Except energy producing materials and support service activities.]
THE PETROLEUM (EXPLORATION AND PRODUCTION) ACT, 2008
[<a href="https://old.zambialii.org/zm/legislation/act/2008/10/peapa2008416.pdf">Act</a>]