Elon Musk did not just say he was considering taking Tesla private Tuesday. He said the funding to do so was “secured.”

No one quite knows what that means. And even while Musk and Tesla have clarified some of the questions behind Musk’s surprise offer, the mystery of where the funding would come from remains.

Shares of Tesla fell Wednesday as the market became skeptical about this assertion. Several banks or investment funds have said they have no plans to invest in Musk’s scheme and with just about every financial journalism outlet working the phones non-stop for the last 24 hours, no one has tracked down any source of funds for a Tesla buyout. Even at the height of the frenzy following Musk’s tweet, the share price never approached the amount offered–a sign that the market is skeptical he can or will follow-through.

As we reported this morning in Pro Rata: Those not involved in Tesla financing include Apple, SoftBank, Uber, TPG, Silver Lake, Mubadala, KKR and basically every large Wall St bank. — Dan Primack (@danprimack) August 8, 2018

Musk said he would offer $420 a share for the company, which would give the company a market cap of over $71 billion. Throw in the debt, and the deal gives Tesla an enterprise value of around $82 billion.

One source of funding would be Musk himself. He owns about 20 percent of the company and has said he expects his stake would not increase in the transaction. That sounds like he’s planning on converting his shares of Tesla into shares of the private investment fund he mentioned would be open to current shareholders. Subtract his stake and Tesla needs $57 billion to take out the equity.

Putting aside the possible legal objections to this investment fund structure, it’s likely that a significant portion of shareholders would opt into the investment fund. If they are holding shares at the current valuation, many of them are clearly bulls on Tesla’s future. They don’t want to be locked out of future gains. What’s more, for many investors there’s likely a significant capital gains tax advantage to converting rather than taking the cash. If you take the cash, you’ll owe tax payments on your capital gains and be locked out of Tesla forever. If you take the conversion, you won’t face a tax bill and you will still get to dream of electric car wealth at night.

But the Tesla investment fund is not without its downside. It will be illiquid, nontradeable. Presumably, the structure would allow investors some opportunity to exit at approved times or under certain circumstances. Investor rights and access to information will likely be highly curtailed. After all, one of Musk’s stated goals is to get out of quarterly reporting.

The top ten institutional investors in Tesla collectively own about 39.6 percent. Many of them are permitted to invest in private companies. It is possible that Musk has talked to these investors and received assurances that they would convert into the private fund. That would be the equivalent of providing around $28 billion of capital to the take private deal–around half of what Musk needs.

So where would the rest of the money come from? One possibility is cash-laden American tech companies. A company like Apple could see this as a path into the “car of the future” race with Google, Uber, and others. Except that Axios’ Dan Primack already confirmed it is not Apple. Google parent Alphabet could also be an investor. Hardware companies could look at this as an opportunity to partner with a company that is already making “smart cars.” Microsoft, Cisco, Oracle, Qualcomm, and Intel all have significant amounts of cash on their balance sheets.

Another possible source of funds: sovereign wealth funds. Ironically, Tesla might be most attractive to funds whose wealth is oil-based. Tesla would allow them to participate in the upside of electric cars and solar power that is a threat to oil wealth. The Saudis recently bought $2 billion of Tesla, according to media reports. Funds from all over the Gulf region are likely to want to follow. Norway’s gigantic $1 trillion pension fund is hugely vulnerable to a turn against oil. Diversifying into electric cars might make sense.

China has a huge amount of cash in its sovereign wealth fund. And Musk recently struck a deal to build a factory in China–and no one knows where the financing for that is coming from. It could be that the notion of taking Tesla private has already been broached with the Chinese. But this might provoke backlash from U.S. regulators, although as long as the Chinese fund doesn’t acquire too big of a stake, it’s unlikely that it would be blocked.

This is all just speculation, of course. But it does demonstrate that it is not impossible for Musk to raise the funds to take Tesla private even if he has to do it without borrowing.