MUMBAI. June 28. KAZINFORM. Kazakhstan-based KazStroyService will make an open offer for an additional 20% stake in Petron Engineering Construction at Rs 180 per share. According to a release issued by Petron to the BSE today, the offer will open on August 14 and close on September 3. Petron's founders had, last week, agreed to sell their controlling stake to KazStroy for an undisclosed sum. The shares of Petron were trading at Rs 188 on the BSE, Kazinform cites Business Standard.