(1) Primarily the result of increased December production in 2019 as compared to the same period in 2018. (2) Primarily the result of a net decrease in fair value of our derivative contracts expected to settle over the next 12 months due to increased oil price futures. (3) At December 31, 2019, we had received advances of $2.5 million related to our Eagle Ford drilling and completion activities and $9.0 million related to our Midland drilling and completion activities. We expect that changes in receivables and payables related to our pace of development, production volumes, changes in our hedging activities, realized commodity prices and differentials to NYMEX prices for our oil and natural gas production will continue to be the largest variables affecting our working capital. We expect to finance future development activities with cash flows from operating activities, borrowings under the Credit Agreement and, various means of corporate and project financing. In addition, as indicated above, we may continue to partially finance our drilling activities through the sale of participating rights to financial institutions or industry participants, and we could structure such arrangements on a promoted basis, whereby we may earn working interests in reserves and production greater than our proportionate share of capital costs. In July 2019, we entered into a Wellbore Development Agreement (“WDA”) with a non-affiliated industry partner. This WDA will reduce our working interest in certain wells in Reagan County. The industry partner is obligated to pay a promoted (proportionately higher) share of the capital expenditures on an initial eight wells, with an option to participate, on the same basis, in up to 11 additional wells, to earn 35% of the working interest in these wells. Capital Expenditures 53 December 31, 2019 2018 Change Current assets: Cash $ 13,822 $ 376 13,446 Accounts receivable: Oil, natural gas, and natural gas liquids revenues 29,047 13,683 15,364 (1) Joint interest billings and other, net of allowance of $83 and $134 at December 31, 2019 and 2018, respectively 6,672 4,166 2,506 Derivative asset 8,860 43,888 (35,028) (2) Prepaid expenses and other current assets 1,867 1,443 424 Total current assets 60,268 63,556 Current liabilities: Accounts payable $ 25,284 $ 26,452 (1,168 ) Revenues and royalties payable 35,815 28,748 7,067 (1) Accrued expenses 19,538 22,406 (2,868 ) Asset retirement obligation 308 557 (249) Derivative liability 6,889 528 6,361 (2) Advances 11,505 3,174 8,331 (3) Operating lease liability 570 — 570 Finance lease liability 206 — 206 Other current liability 43 — 43 Total current liabilities 100,158 81,865 Working Capital $ (39,890) $ (18,309) (21,581)