Abstract: The detonation gas for gas-detonatable blasting charges used in surface mining and the like is supplied by a portable self-contained delivery unit connected to the blasting charges by a network of small flexible tubing, which unit blends pressurized fuel and oxidizing gases from separate supply sources in predetermined proportions and regulates the separate flows of such gases in response to the backpressure imposed by the tubing network to maintain such proportions in the gas blend delivered to the tubing network. The separate gas flows are controlled by servo-actuated flow control valves actuated by a control gas pressure which is applied or released in response to such backpressure.