Well, I have received many offers in past years. What I noticed that all these offers were made mainly Oil & Gas companies like BP, Shell, Chevron, Takreer etc. recently one of my friend received an offer from Takreer, but if you visit these companies original websites you can find the reality. you can not find the contact details matching. Even some companies posted on their websites about these scams.
These offers are not from these reputed companies but from scammers. Offers looks very attractive, If you will show interest they will ask you money for visa process, which they will reimburse after joining. They will ask money by western union or online transfer. You can easily identify that such a reputed companies will never ask money for visa process.
My suggestion, try to contact to the companies you got the offers earlier, they may still have the jobs available.