Shares of Hertz Global (HTZ) - Get Report revved higher on Thursday after billionaire investor Carl Icahn revealed his activist investment firm has increased its stake in the car-rental giant.

Shares of the Estero, Florida-based company were up 1.18% at $14.56 in morning trading on Thursday after rising as high as $15 in premarket trading after a 13-D Securities and Exchange Commission filing disclosed that several of Icahn's funds, including Icahn Capital LP and Icahn Partners Master Fund LP, had purchased additional shares of Hertz.

In total, Icahn's stake in the company is now 30.1% from 29.5%.

To be sure, Icahn has adjusted his stake in the car and truck rental giant up and down before. In March, Icahn cut his Hertz holdings to the 29.5% level following better-than-expected quarterly results

Hertz in August posted second-quarter adjusted profit of 74 cents a share compared to losses of 17 cents a year ago, well ahead of Wall Street forecasts of earnings of 22 cents a share. 

Sales hit $2.5 billion in the three months through June 30, up 5% from $2.4 billion the year before.