Hazardous substance tax

The Hazardous Substance Tax (HST) is a tax on the possession of hazardous substances in Washington. The tax is imposed on the first possessor of the hazardous substance in Washington and is paid directly to the department.

HST applies to many pesticides, petroleum products, and chemicals used in the agriculture and farming industry.

Are farmers exempt from this tax?

Farmers are not generally exempt from this tax. The tax is on the first possessor of a hazardous substance and does not apply to subsequent possessors when the tax has already been paid. If you purchase hazardous products from an in-state supplier, your billing from the supplier may indicate that the HST was paid and that it is being passed on to you.

If you purchase the hazardous substance from an out-of-state supplier who has not paid Washington's HST, then you owe the tax as the first possessor in this state.

How do I pay the tax?

The tax is reported on the Excise Tax Return. There are two separate lines on the return to report each HST rate.

What rate do I pay?

Petroleum products measured on a per barrel basis are subject to a per barrel (42 gallons) rate according to the table below. For these products, use the Hazardous Substance Tax by Volume line.

Period	Tax rate per barrel
July 1, 2024 - June 30, 2025	$1.48
July 1, 2023 - June 30, 2024	$1.40
July 1, 2022 - June 30, 2023	$1.20
July 1, 2021 - June 30, 2022	$1.14
July 1, 2020 - June 30, 2021	$1.13
July 1, 2019 - June 20, 2020	$1.09

Note: The per barrel rate on petroleum products will be adjusted for inflation on July 1 each year.

Petroleum products not easily measured on a per-barrel basis:

That remain in a liquid state at standard temperature and pressure of 25°C (or 77°F) and 1 atmosphere (or 14.7 pounds per square inch) are subject to HST on a per barrel basis according to the table above. For these products, use the Hazardous Substance Tax by Volume line.

That do not remain in a liquid state under these conditions will continue to be taxed at a rate of 0.7 % (0.007) multiplied by the wholesale value of the petroleum product. For these products, use the Hazardous Substance Tax by Value line.

Non-petroleum products are subject to a rate of 0.7% (.007) multiplied by the wholesale value of the products. For these products, use the Hazardous Substance Tax by Value line.