Carry-over of salt-laden aerosols into flares at upstream oil and gas production sites is a potentially important driver of adverse flare emissions. However, the frequency of this occurrence at upstream production sites is unknown. Sodium (Na) and potassium (K) are abundant in produced water samples and have persistent atomic emission signatures at 588/589 and 766/769 nm. A pair of spectrometer systems was developed to detect these signatures in flare flames as proof of liquid carry-over. Field measurements of 95 flares at upstream oil and gas production sites in North Dakota, Saskatchewan, and Ecuador found 72% had detectable Na or K signatures, suggesting liquid carry-over is surprisingly common. Analysis of the 76 North Dakota flares found that liquid carry-over was statistically correlated with younger wells and increased volumes of produced oil, water, gas and reported flared/vented volumes. These findings have importance implications for the likely severity of global flare emissions.