Opera has found that, on average, over 30% of all mobile data is used by apps running in the background.
Facebook Messenger and Gmail are the most data-hungry apps in this way, with 73% of their total data usage happening in the background.
Google Drive and WhatsApp showed more than 50% background data usage.
It said its findings are based on anonymous aggregated statistics collected from millions of Opera Max users in December 2015.
“Most apps are made to give a great user experience, not to save data. If you fetch background data through your data plan, it’s like throwing away $1 out of every $3 you spend,” said Sergey Lossev, product manager at Opera Software.
“Most people are not aware of this background data drain and may not have authorized it, nor do they know how to stop it from happening.”
Opera said it has built Smart Alerts into Opera Max to help smartphone users manage their background data usage.