35 ILCS 450/2-45
Each purchaser shall make a return to the Department showing the quantity of oil or gas purchased during the month for which the return is filed, the price paid therefor, total value, the name and address of the operator or other person from whom the same was purchased, a description of the production unit in the manner prescribed by the Department from which such oil or gas was severed and the amount of tax due from each production unit for each calendar month. All taxes due, or to be remitted, by the purchaser shall accompany this return. The return shall be filed on or before the last day of the month after the calendar month for which the return is required. The Department shall forward the necessary information to each Chief County Assessment Officer for the administration and application of ad valorem real property taxes at the county level. This information shall be forwarded to the Chief County Assessment Officers in a yearly summary before March 1 of the following calendar year. The Department may require any additional report or information it may deem necessary for the proper administration of this Act.
Such returns shall be filed electronically in the manner prescribed by the Department. Purchasers shall make all payments of that tax to the Department by electronic funds transfer unless, as provided by rule, the Department grants an exception upon petition of a purchaser. Purchasers' returns must be accompanied by appropriate computer generated magnetic media supporting schedule data in the format required by the Department, unless, as provided by rule, the Department grants an exception upon petition of a purchaser.
If any payment provided for in this Section exceeds the purchaser's liabilities under this Act, as shown on an original return, the purchaser may credit such excess payment against liability subsequently to be remitted to the Department under this Act, in accordance with reasonable rules adopted by the Department.
35 ILCS 450/2-45