Eleven grassroots political action committees – spanning environmental, business and social-justice organizations – have organized to fight Prop. 23, the November ballot measure that would freeze California’s landmark climate change law. Together they’ve raised more than $15.6 million, as of the Oct. 5 campaign finance disclosures.

But only one PAC is driving the Yes on 23 campaign, which has built a total war chest of almost $8.4 million. Most of that comes from oil and gas companies, primarily Texas’ Valero and Tesoro.

One pair of very, very rich brothers is operating the biggest gears behind the Prop. 23 curtain. Meet David and Charles Koch, the Texas Libertarians and Tea Party faithfuls who, according to a recent profile in The New Yorker, are together worth more than $35 billion and have “quietly given more than $100 million to right-wing causes.” They’ve consistently thrown their money against health-care reform, regulation of polluting industries and progressive climate change policies – including California’s AB 32.

Prop. 23’s top contributors, as of Oct. 5:

1. Valero Services ($4,060,000)

2. Tesoro Companies ($1,525,000)

3. Flint Hills Resources ($1,000,000)

4. Adam Smith Foundation ($498,000)

5. Occidental Petroleum Co. ($300,000)

6. Tower Energy Group ($200,000)

7. No New Taxes, a project of the Howard Jarvis Taxpayers Association ($103,000)

8. National Petrochemical & Refiners Association ($100,000)

Source: cal-access.ss.ca.gov. Figures rounded to the nearest thousand.