Glaciers in the Southern Patagonia Icefield (SPI) have been shrinking in recent decades, but due to a lack of field observations, understanding of the drivers of ablation is limited. We present a distributed surface energy balance model, forced with meteorological observations from a west-east transect located in the north of the SPI. Between October 2015 and June 2016, humid and warm on-glacier conditions prevailed on the western side compared to dry and cold conditions on the eastern side. Controls of ablation differ along the transect, although at glacier-wide scale sensible heat (mean of 72 W m-2 to the west and 51 W m-2 to the east) and net shortwave radiation (mean of 54 W m-2 to the west and 52 W m-2 to the east) provided the main energy sources. Net longwave radiation was an energy sink, while latent heat was the most spatially variable flux, being an energy sink in the east (-4 W m-2) and a source in the west (20 W m-2). Ablation was high, but at comparable elevations, it was greater to the west. These results provide new insights into the spatial variability of energy-balance fluxes and their control over the ablation of Patagonian glaciers.