GM's $152.3 billion in revenue was less than a third of that of the first company on the list: Wal-Mart, which regained the title from Exxon Mobil. Berkshire Hathaway and Apple are the firms that moved GM down. Ford, displaced by energy company Valero, had $134.3 billion in revenue.
On a side note, profitability isn't a factor, but both GM and Ford were down in this year's list compared to last year's: GM declined from $9.2 billion to $6.2 billion, Ford fell from $20.2 billion to $5.6 billion. If profits were included, Exxon Mobil would probably still be king: although the energy company made almost $20 billion less in revenue than Wal-Mart's $469.2 billion, it posted $44.9 billion in profit compared to Wal-Mart's $17 billion.