The Caltex brand, which serves customers in Asia, the Middle East and Africa, is managed from the city-state.
Convertium will take on work for Singapore, Malaysia, Philippines, Thailand, Cambodia, Hong Kong, New Zealand, Pakistan and South Africa.
The local digital shop will be working with Caltex's global marketing team to deliver enhanced web experiences to customers via a range of online content and services for motoring consumers.
According to a statement, at present, Caltex enjoys 800,000 visitors to its various sites every day. The aim is to grow this number by leveraging on the human experience in daily motoring, and delivering online values that fulfil the changing needs of the motoring public in each market.
Besides product information, consumers can expect daily motoring tips and tools to enhance their motoring lifestyle.
Convertium will be responsible for the user experience, content architecture, user interface design, applications development, and search optimisation of the websites.
The new websites will be rolled out by the fourth quarter of this year.
On the appointment, Gerard Lim, managing director of Convertium, said: "Our team is all charged up with this assignment. The Caltex brand is especially famous in this hemisphere, and we look forward to enhancing its web presence to better serve more customers."
He added: "The multi‐country brief also challenges us to think way beyond Singapore and deliver a web solution that is consistent with the Caltex brand values and yet relevant to each specific market."