Elon Musk’s string of Tesla Inc. share sales carried on a fourth consecutive day, bringing the total the chief executive officer has offloaded in the wake of an unusual public poll to about US$5.7 billion. 

The billionaire disposed of 639,737 shares on Thursday worth about US$687 million, according to regulatory filings. He unloaded US$5 billion of stock earlier in the week after asking his Twitter followers whether he should sell 10 per cent of his Tesla stake.

The poll was controversial for a host of reasons. For one, some of Musk’s transactions were carried out this week under a trading plan he pre-arranged in September, well before he consulted his vast social media following. Musk also cast his proposal as having to do with the debate raging in the U.S. over whether billionaires are paying enough in taxes, and whether levies should be placed on unrealized capital gains.

Musk also didn’t mention in his weekend tweets that he has millions of stock options that must be exercised before they expire in August 2022. He said in September that he was likely to sell “a huge block” of those options toward the end of this year.

Tesla shares slipped as much as 0.8 per cent before the start of regular trading Friday. The stock has slumped 13 per cent this week.

The documents disclosing Musk’s sales this week shed no light on whether his poll had any bearing on his decision to carry out some or all of the transactions, or whether he’ll keep selling until he’s met the 10 per cent threshold. To get there, he’d have to get rid of roughly 17 million shares, and even more if he also includes exercisable options in his total ownership. He’s now disposed of about 5.2 million shares.

One of Tesla’s most outspoken bulls on Twitter has been critical of how Musk has carried out the sales. Gary Black, a managing partner at investment adviser The Future Fund LLC, has called out the CEO for costing himself money and dragging out the process.

Musk, 50, is the world’s richest person with a net worth of US$294 billion, according to the Bloomberg Billionaires Index.