By midafternoon, shares had climbed 14.7% to $4.18.
Trading volume of 8.7 million had exceeded its three-month daily average of 5.7 million.
The Sao Paulo-based steel company said it will repurchase up to 70.2 million shares from March 14 to April 14.
In a statement, the company said the buyback's objective is to "maximize the creation of value to shareholders by means of an efficient capital structure management."
Companhia currently has 1.46 billion shares outstanding.
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TheStreet Ratings team rates COMPANHIA SIDERURGICA NACION as a Hold with a ratings score of C. The team has this to say about their recommendation:
"We rate COMPANHIA SIDERURGICA NACION (SID) a HOLD. The primary factors that have impacted our rating are mixed -- some indicating strength, some showing weaknesses, with little evidence to justify the expectation of either a positive or negative performance for this stock relative to most other stocks. The company's strengths can be seen in multiple areas, such as its expanding profit margins and notable return on equity. However, as a counter to these strengths, we also find weaknesses including unimpressive growth in net income, weak operating cash flow and a generally disappointing performance in the stock itself."
Highlights from the analysis by TheStreet Ratings Team goes as follows: