The Washington Post published a front page story on Wednesday looking at the plummeting tax rates paid by the 30 firms represented in the Dow Jones Industrial Average, providing a microcosm of the rampant tax avoidance by corporate America.

With 26 of the corporations seeing a decreased tax rate over the past decades, including 22 companies whose rates have declined more than 10 percentage points, the Post writes that the rise of multinational corporations and an antiquated tax code last overhauled in 1986 provide an “unprecedented ability” for companies to shift their profits across national borders to avoid U.S. taxes:

“Experts say the U.S. code has encouraged companies to shift their income overseas, where it is more lightly taxed by the U.S. government. […] The result is lower revenue here that could pay for infrastructure, education and other services that support domestic growth — and that make life easier for U.S. firms.”

The Post does not delve into what might account for the failure of Congress to update to a fairer tax code that would put large multinationals on a more level playing field with smaller, domestic-focused companies, but looking at the political influence of the Dow 30, it’s hard to imagine that their status as lobbying giants does not play a part.

Since 1998, the Dow 30 have collectively spent over $2.2 billion dollars lobbying the federal government, based on Public Campaign analysis of data from the Center for Responsive Politics, making them some of the most represented interests in the halls of Congress. For context, that’s more money than the combined spending of all lobbying interests combined in any single year between 1998 and 2004. In a gridlock-prone political system where killing legislation is usually easier than passing it, the Dow 30’s swarms of lobbyists have certainly helped prevent tax code changes that would make tax avoidance more difficult.

From a financial perspective, this strategy is a shrewd investment. For example, the Post reports that a Senate committee found that just in the three years from 2009 to 2011, Microsoft was able to avoid paying $4.5 billion in taxes on U.S. retail sales by offshoring intellectual property rights. If Microsoft’s $106 million in lobbying expenditures since 1998 had anything to do with keeping that loophole open, that would be the kind of return on investment usually found only in a business executive’s dreams.

Even with this lucrative status quo, multinationals have continued to push the envelope for tax policies that would let them pocket even more money. Corporate-backed groups like the Fix the Debt coalition have been advocating policies like a lower corporate income tax and a “territorial” tax system that would let companies bring profits back from overseas—profits that might have been offshored to avoid U.S. taxes in the first place—without paying taxes to the U.S. government. Public Campaign released a report last fall examining the campaign contributions and lobbying expenditures flowing from Fix the Debt companies, and the Institute for Policy Studies found that 63 corporations backing Fix the Debt could stand to gain $134 billion under the territorial tax policy.

Here are the amounts spent on lobbying by each of the 30 firms in the Dow Jones Industrial Average: