Guar seed prices on Monday rose by Re 1 to Rs 3,900 per 10 quintal in futures trade after speculators increased their positions driven by a firm trend in spot market. On the National Commodity and Derivatives Exchange, guar seed for January contracts increased by Re 1, or 0.03 per cent, to Rs 3,900 per 10 quintal with an open interest of 19,375 lots. According to marketmen, raising of bets by speculators tracking a firm trend in spot market on thin supplies from growing belts mainly led to the rise in guar seed prices here. However, guar seed for February delivery traded lower by similar margins to Rs 3,948 per 10 quintal with an open interest of 45,920 lots.