Andrew Tinkler and William Stobart, chief executive and chief operating officer respectively, have sold a significant chunk of their stakes in the logistics group to 'satisfy strong institutional demand'.
The bulk of the shares, more than 7m, were sold by Stobart Air Holdings, a company controlled by Andrew Tinkler and William Stobart, at 149p a share, realising £10.5m for the pair.
Stobart Air Holdings no longer holds an interest in Cumbria-based Stobart Group.
In a separate transaction, Tinkler also sold 2m shares at 149p a share, raising £2.9m.
The shares have performed well during the past year, rising from 108p in August 2009 but are down slightly from the year high of 162p in April this year.
Tinkler still holds 28.48m shares, representing 10.74% of the company's issued share capital. His stake is valued at £42m.
Other directors also sold shares in Stobart last week. Ben Whawell, finance director, offloaded 30,000 shares on 4 August at 149p a share, raising £44,700 'for a forthcoming property purchase'. Whawell remains interested in 67,906 shares, representing 0.026% of the company's issued share capital. Richard Butcher, deputy chief executive, made £131,000 from the sale of 88,500 shares on 5 August at 148.5p a share, also to fund a forthcoming property purchase. Butcher remains interested in 3,880 shares, representing 0.0015% of Stobart's share capital.