An Equinor ASA subsidiary is entitled to a $4.5 million refund of taxes it paid on natural gas liquids extracted in West Virginia because the tax department improperly calculated the gas’s value, the state high court ruled Friday.

The state tax commissioner asked the West Virginia Supreme Court of Appeals to overturn an appellate court decision that Equinor USA Onshore Properties Inc. overpaid mineral severance taxes for four tax years. The appellate court said the state miscalculated the gross value of the butane, propane, methane, and ethane Equinor sold to a midstream buyer.

The justices affirmed, agreeing with Equinor the …