In a press release about its investment, Siemens said: "The participation of Siemens in this project is permissible under the applicable laws and regulations and does not infringe the right of self-determination or any other human right in public international law".
William Hayes, senior vice president of Kosmos Energy, tells This is Africa his that exploration offshore Western Sahara is "fully consistent with international law and the 2002 UN Legal Advisor's Opinion", adding that the company has taken the territorial issue seriously. "From the very beginning of our involvement in the territory, we have spent both time and resources to develop a deep knowledge of the complex and nuanced situation in Western Sahara."
Mr Hayes says the Moroccan government will keep to its side of the bargain by ensuring revenues, if exploration is successful, benefit the people of the region.
"In our discussions with ONHYM [the Moroccan national oil company] regarding our exploration activities, it is evident to us that Morocco is paying increasing attention to consultation, transparency and resource governance models," he claims.
But Kamal Fadel, spokesperson for the SADR Petroleum and Mines Authority, says no companies have contacted them about their investments at all - and he is sceptical that revenue resources will be allocated to the Saharawi people as the international law demands.
"Payments for resources from occupied Western Sahara are not returned to the territory. They are paid to the central Moroccan state treasury in Rabat.
Any deals made with Morocco involving Western Sahara would only be a source of employment for Moroccan nationals settled into the territory. Any deals with Morocco involving Western Sahara will only serve to legitimise and entrench Morocco's illegal occupation and serve as pretext for seemingly normal commercial activity," he tells This is Africa.
Either way, any commercial deals will likely not benefit the roughly 165,000 Saharawis who have fled to refugee camps in southwest of Algeria.
The EU accord seems to lend strength to the legitimacy of Morocco's claim, but the country has no jurisdiction in Western Sahara, Mr Fadel says. "No country in the world recognises Morocco's sovereignty over Western Sahara and the UN does not even consider Morocco as the administering power, while the Saharawi republic is a member of the African Union and is recognised by more than 80 states worldwide," he says.
The SADR is considering legal action against the companies investing in the territory, including long-term future compensation claims.
Mr Fadel says all deals signed with Morocco "will be considered null and void" when the Saharawi republic achieves its full sovereignty. The EU and international firms seem to be betting that day won't come.
Additional reporting by Tom Stevenson