13. Financial Instruments and Derivatives

Financial Instruments. The estimated fair value of financial instruments at December 31, 2019 and December 31, 2018, and the related hierarchy level for the fair value measurement is as follows:

(1) Included in the Balance Sheet lines: Notes and accounts receivable, less estimated doubtful amounts and Other assets, including intangibles, net

(2) Included in the Balance Sheet line: Investments, advances and long-term receivables

(3) Included in the Balance Sheet lines: Investments, advances and long term receivables and Other assets, including intangibles, net

(4) Included in the Balance Sheet lines: Accounts payable and accrued liabilities and Other long-term obligations

(5) Excluding finance lease obligations

(6) Included in the Balance Sheet line: Other long-term obligations

(7) Advances to/receivables from equity companies and long-term obligations to equity companies are mainly designated as hierarchy level 3 inputs. The fair value is calculated by discounting the remaining obligations by a rate consistent with the credit quality and industry of the company.

The increase in the estimated fair value and book value of long-term debt reflects the Corporation’s issuance of $7.0 billion of long-term debt in the third quarter of 2019.

Derivative Instruments. The Corporation’s size, strong capital structure, geographic diversity and the complementary nature of the Upstream, Downstream and Chemical businesses reduce the Corporation’s enterprise-wide risk from changes in commodity prices, currency rates and interest rates. In addition, the Corporation uses commodity-based contracts, including derivatives, to manage commodity price risk and for trading purposes. Commodity contracts held for trading purposes are presented in the Consolidated Statement of Income on a net basis in the line “Sales and other operating revenue”. The Corporation’s commodity derivatives are not accounted for under hedge accounting. At times, the Corporation also enters into currency and interest rate derivatives, none of which are material to the Corporation’s financial position as of December 31, 2019 and 2018, or results of operations for the years ended 2019, 2018 and 2017.

Credit risk associated with the Corporation’s derivative position is mitigated by several factors, including the use of derivative clearing exchanges and the quality of and financial limits placed on derivative counterparties. The Corporation maintains a system of controls that includes the authorization, reporting and monitoring of derivative activity.

At December 31, 2019, the net notional long/(short) position of derivative instruments was 57 million barrels for crude oil, (38) million barrels for products, and (165) million MMBtus of natural gas. At December 31, 2018, the net notional long/(short) position of derivative instruments was (19) million barrels for crude oil and was (9) million barrels for products.

Realized and unrealized gains/(losses) on derivative instruments that were recognized in the Consolidated Statement of Income are included in the following lines on a before-tax basis: