Tank emission calculation is normally performed offline and manual data gathering from various tanks could be a timely and inefficient task. This paper presents iCON first principal process simulation software, used to perform tank emission calculations by leveraging on its existing extensive database of all process simulation models and chemical components physical property. Hence, a lot of operation cost is saved by eliminating the need for inventory sampling activity for each tank. This paper also will discuss online tank emission work processes to make it sustainable. iCON Tank Emission complies to United States Environmental Protection Agency (USEPA) Compilation of Air Pollutant Emission Factors (AP-42) Fifth Edition Chapter 7 Liquid Storage Tanks that covers fixed roof tanks (vertical and horizontal) and floating roof tanks (internal, external and domed) with respective combination of roof, shell, rim seal, fittings and breather vent settings. It is also linked to monthly Malaysian Climate Condition that covers domestic municipals temperature (minimum and maximum), Solar Irradiance Factor and wind speed that improves the tank emission calculation accuracy. iCON Tank Emission lets users calculate thousands of tank emission simultaneously by using iCON communication (COM) interface feature and displays the results in monthly and yearly summary for report standardization among multiple business units. The average simulation convergence time is 100 tanks simultaneous calculation per minute making it time efficient for HSE engineers to perform strict monthly calculation and reporting. Case studies and what if scenarios could also be run in effort to reduce tank emission via introduction of vapor recovery and optimizing tank mechanical parameters i.e. type of rim seal, color and fittings selection. iCON Online Tank Emission is working through linking iCON model with real time plant information data for real time tank emission calculation which is transparent to management and regulators. The findings from this compositional first principles thermodynamic base tank emission simulation study are considered more efficient, faster and cheaper than conventional method.