Tesla Inc. has more money in the bank than ever, which could bejust the assurance credit raters have been waiting for to upgradethe company's bonds.

The electric-carmaker ended the fourth quarter with a record US$6.3 billionof cash, up nearly $1 billion from the third quarter. It's alsostrung together three straight quarters of positive cash flow. Thatfigure topped $1 billion in the latest quarter, helping to send itsshares to record highs, which in turn could make more than $4billion of its bonds eligible to convert to equity.

S&P Global Ratings rates Tesla B-, six steps belowinvestment-grade, with a positive outlook. It said in November itcould upgrade the company if—among other factors—free cash flow isat least around break-even and cashis $2.5 billion or more. Moody's Investors Service has outlinedsimilar upgrade criteria.