Corporate lobbying apparently pays off big-time for shareholders.

Strategas Research Partners' Lobbying Index, which measures the stock performance of the 50 companies that spend the most money on lobbying, has beaten the Standard & Poor's 500 Index for 15 years in a row, CNBC.com reports.

"In our opinion, this consistent outperformance suggests that the market cannot properly value the return from company lobbying activities," the firm says in a report obtained by the news service.

Editor's Note: Secret Wall Street Calendar Uses Strange ‘Crash Alert System,’ Gets 18.79% Annual Returns

The Lobbying Index generated an average annual return of 17.4 percent in 2012 and 2013, compared to 6 percent for the S&P 500, according to Strategas.

Corporate spending on lobbying totaled $3.21 billion in 2013, according to the Center for Responsive Politics, CNBC.com reports. Financial companies led the way with $484.6 million, followed by the healthcare sector with $480.3 million.

The Lobbying Index includes the companies that spend the most on lobbying as a percentage of their assets, and few of them are in finance.

The top five spenders in the index are 3M, Accenture, Alexion Pharmaceuticals, Altria and Brown-Forman. The industrial sector contributes the most companies to the index — 10.

Online brokerage firm Motif Investing offers a pool of 20 stocks it calls "Kings of K Street." Like the Strategas index, the Motif pool includes companies which "tend to spend the most on lobbyists relative to the size of their asset bases," Motif says on its web site.

The pool's biggest holdings are American Airlines, Orbital Sciences and Lockheed Martin. It has a one-year return of 40.3 percent.

Editor's Note: Secret Wall Street Calendar Uses Strange ‘Crash Alert System,’ Gets 18.79% Annual Returns

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• Google Amassing Army of Lobbyists to Sway Capitol Hill