An experimental study is presented of a spray atomizer used in heavy oil upgrading. Bubble size in the feed flow was observed to determine its influence on the atomization of an effervescent nozzle. Experiments were conducted with water and air in a two-phase flow, commercial-scale facility at ambient conditions (horizontal air/water bubbly feed in a 25.4 mm tube to a single contraction throat diameter of 12.7 mm). Different mixtures were tested with water flow rates from 113 to 200 kg/min and 1 to 4 kg/min for air flow rate, achieving an air liquid ratio, gamma, from 1% to 4%. The range of feed parameters would result in flow regimes that were either bubbly or intermittent in equilibrium horizontal flow. Two bubble breakers (perforated plates) were used to modify the size of the bubbles in the conduit feeding the nozzle. Bubbles and droplets were measured with visualization techniques using front lighting for bubbles and shadowgraphy for droplets. A single location in the spray cone was chosen as the characteristic location in the flow where droplet size and distribution are most representative of the mass flow of the spray liquid. Acquired images were used to estimate the size and shape and calculate Sauter mean diameter. The experiments indicate that the influence of the scale of bubbles in the feed on the reduction of droplet size resulted in the atomization and support the need for attention in designing the feed delivery premixing and transport to the nozzle.