Transocean Barents, an oil platform passes through Canakkale Strait as vessel traffic suspended in both directions in Canakkale, Turkiye on November 12, 2024. Enishan Keskin | Anadolu | Getty ImagesShares of Transocean plunged Thursday after the offshore driller announced the sale of a large number of shares at a discount.Transocean is planning to sell 125 million shares at a price of $3.05, significantly lower than Wednesday's close of $3.64. It is offering 25 million shares more than it originally planned.The Swiss company's stock closed 13% lower at $3.16 per share. The offering is expected to close on Friday.Transocean expects to book about $381 million from the sale. It will use the proceeds to pay off debt.(Correction: Updates with correct share offering price.)