Share buybacks have been helping keep the bull market afloat - these 8 companies have contributed the most

• Companies who were flush with cash started to buy back shares after the S&P 500 started to recover from the global financial crisis.
• Buybacks cut a company's total share count, and spread the profits over fewer shares, boosting their per-share earnings.
• Over the past decade, S&P 500 companies bought back $4.4 trillion shares, including the record-breaking buybacks from Apple that totaled $226.6 billion.
• Share buybacks are expected to continue growing for the coming months, according to an analyst from S&P Dow Jones Indices.

For the 9-1/2-year equity bull run, share buybacks have been a solid backbone of the stock market's continued growth. Buybacks cut a company's total share count, and spread the profits over fewer shares, boosting their per-share earnings and satisfying Wall Street.

After the S&P 500 started to recover from its financial crisis low in March 2009, companies that were flush with cash started to buy back shares. According to S&P Dow Jones Indices, S&P 500 companies have bought back $4.4 trillion shares over the past decade, including the record-breaking buybacks from Apple that totaled $226.6 billion. No company has bought back more shares than Apple, which announced in March 2012 it would use a large chunk of cash to make the purchases.

The amount in share repurchases executed by S&P 500 companies hit a record of $190.6 billion in the second quarter, a 58.7 % year-over-year increase, and that number is expected to keep growing for the coming months, according to S&P Dow Jones Indices.

"Given the record earnings, strong cash-flow, investor demand and corporate statements, the indications are that the high level will continue for the rest of the year," said Howard Silverblatt, senior index analyst at S&P Dow Jones Indices.

Here are the top eight companies that contributed $689.4 billion, or 16% of the total S&P global 500 companies buybacks, mostly from the information technology and financial sectors.