Do any airlines use low emissions fuels?

• https://www.reuters.com/article/us-ual-emissions/united-airlines-targets-50-percent-cut-in-greenhouse-gas-emissions-idUSKCN1LT32A
• https://www.theguardian.com/business/2019/sep/19/aviations-flight-towards-low-emissions-only-fuels-the-crisis
• https://www.vox.com/energy-and-environment/2019/1/11/18177118/airlines-climate-change-emissions-travel