We are party to derivative contracts through certain of our subsidiaries. Currently, the most significant derivative contracts consist of equity index put option contracts. The liabilities and related notional values of these contracts follows (in millions).

Liabilities

Notional

Value

September 30, 2019

1,236

23,042

December 31, 2018

2,452

26,759

Notional value represents the aggregate undiscounted amounts payable assuming the value of each index is zero at each contract’s expiration date. Certain contracts are denominated in foreign currencies and the related notional amounts are based on the foreign currency exchange rates as of the balance sheet date. Pre-tax gains from equity index put option contracts were $234 million and $1,217 million in the third quarter and first nine months of 2019, respectively, and $137 million and $303 million in the third quarter and first nine months of 2018, respectively.

The equity index put option contracts are European style options written prior to March 2008 on four major equity indexes. The remaining contracts expire between October 2019 and October 2025. The weighted average life of unexpired contracts at September 30, 2019 was approximately 1.3 years. Contracts with notional values of $9.0 billion will expire in the fourth quarter of 2019. Future payments, if any, under any given contract will be required if the prevailing index value is below the contract strike price at the expiration date. We received aggregate premiums of $3.6 billion on the contract inception dates with respect to unexpired contracts at September 30, 2019 and we have no counterparty credit risk. The aggregate intrinsic value (the undiscounted liability assuming the contracts are settled based on the index values and foreign currency exchange rates as of the balance sheet date) was $626 million at September 30, 2019 and $1,653 million at December 31, 2018. These contracts may not be unilaterally terminated or fully settled before the expiration dates and the ultimate amount of cash basis gains or losses on these contracts will not be determined until the contract expiration dates.

A limited number of our equity index put option contracts contain collateral posting requirements with respect to changes in the fair value or intrinsic value of the contracts and/or a downgrade of Berkshire’s credit ratings. As of September 30, 2019, we did not have any collateral posting requirements. If Berkshire’s credit ratings (currently AA from Standard & Poor’s and Aa2 from Moody’s) are downgraded below either A- by Standard & Poor’s or A3 by Moody’s, collateral of up to $1.1 billion could be required to be posted.

Our regulated utility subsidiaries are exposed to variations in the prices of fuel required to generate electricity, wholesale electricity purchased and sold and natural gas supplied for customers. We may use forward purchases and sales, futures, swaps and options to manage a portion of these price risks. Most of the net derivative contract assets or liabilities of our regulated utilities are probable of recovery through rates and are offset by regulatory liabilities or assets. Derivative contract assets are included in other assets and were $144 million as of September 30, 2019 and $172 million as of December 31, 2018. Derivative contract liabilities are included in accounts payable, accruals and other liabilities and were $96 million as of September 30, 2019 and $111 million as of December 31, 2018.