So lemme try have some discussion on this matter.
• Russian interests in Syria:
The Syrian city of Tartus happens to be home to the only Russian naval base in the Mediterranean, allowing them continuous naval presence in the area. Without it the entire sea would essentially be dominated by NATO members, and Russian influence in the Middle East would drop. It's in Russian interests to keep Assad's regime in power, as otherwise their naval influence could be seriously hindered.
• To the mentions about US interests in Syrian oil:
This seems very improbable. Just look at Libya, which has about 25% more oil production than Syria, and definitely would have presented an easier target if the aim was to capture oil. The last time I checked, US wasn't in control of Libyan oil. (Besides, US still has a huge oil production of its own, in addition to Western oil companies dominating Iraqi oil production)
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People should be careful when making statements about the situation in Syria. The country is in war, and certain information is hardly available as there isn't much room for any 'independent' media networks.
As far as the gas strike goes, I'd say the most solid evidence and information at the moment is from Doctors Without Borders, confirming that there has been a chemical strike, however the organization has clarified that there is no clear indication or information on the origin of the strike, as also reportedly said in the UN report regarding war crimes in Syria. Sure, it is known that Assad does possess chemical weapons, but knowing the country is a clusterforget makes it entirely feasible that other factions might have access to these kinds of weapons. (hell, they could even be smuggled from god knows where)
The gas reportedly used in the strike was sarin, which is relatively easily available. Ever heard of the gas attack on a Tokyo subway in 1995? The dude also used sarin. Makes it all the more tougher to pinpoint the origin of the strike in Syria.
I'm pretty doubtful that US intelligence has some kind of secret superreliable info showing beyond reasonable doubt that Assad's regime performed the strike, if even UN with investigators in the area isn't certain of the origin of the strike. Intelligence agencies like CIA rely mainly on informants, and there's no way they will be 100% reliable, especially during a war.
As an endnote, I hope the arrangement to set Assad's chemical weapons under surveillance works out, as based on the information available, threats towards his regime on grounds of having performed a chemical strike seem unfounded at the moment. (Not like there isn't a stuffpile of other reasons to attack his regime ... though bear in mind those opposing the gov't aren't exactly angels either. War is war and the groups fight for their own interests.)
tl;dr: never ever put cologne on your balls
