Ultramar Group is a port agency serving shippers in ports in Peru, Chile, Argentina, Brazil, and Uruguay.
The company´s site shows the company's house flag, per saltire white and blue with a blue ring surrounding a white disk on the center, and the letter U on it in blue.
It seems that the Ultramar HQ is in Argentina.
The World Salvage Directory (http://www.marine-salvage.com/wsd_int.htm) of the International Salvage Union (ISU) lists the member companies and show the house flag of some of them (on each individual company page, linked from the directory). The flag of Remocaldores Ultragas Ltda. is divided per saltire blue-white-blue-white, with the letter "U" in blue enclosed in a blue circle, in the middle.
the ring is black and the "U" is blue: Apart from the color difference, the ratio is slightly more oblong (5:8 instead of ~2:3), and the ring and "U" are thinner.