Oklahoma Treasurer Ken Miller says overall revenue collections to the state treasury last month hit a six-year low as the state's economy continues to slump.
Miller reported Monday that May collections were lower than May 2015 for every major revenue stream, including taxes on income, sales, motor vehicles and oil and natural gas production.
It is the ninth consecutive month that 12-month gross receipts to the treasury are lower than those for the previous 12-month period.
Miller says Oklahoma's economic contraction is no surprise as it grapples with the "spillover effects" of the declining energy industry.
Oil and gas production tax collections rose slightly in May after hitting a 17-year low in April, but are still lower than May 2015 collections by nearly 37 percent.