Oil is sitting at an interesting point heading into potential US-Iran talks this week.Brent crude is hovering just above the $100 mark as traders took some comfort from hopes of diplomatic progress and signs that Saudi crude shipments are recovering from earlier this week. The fact that $100 is even being eyed again tells you how quickly some of the geopolitical premium can come out when the market sees a possible path towards de-escalation.For me, that makes the next move in oil prices more important than the number itself.We all know the story about rising oil prices and how that will spill over to broader markets, leading to higher bond yields and complicating things for central banks with regards to inflation.But what happens if there is path to the other side, in which oil prices find a sustained break back lower? What would it take to get there? And how feasible would it be that prices actually stick at those levels?Looking at the current situation, a sustained break lower would probably need more than encouraging headlines. Markets would want signs that US-Iran talks are actually reducing the risk around supply in the Gulf region, particularly the Strait of Hormuz. The disruption there is what has kept the physical oil market tight as flows are still not fully back to normal and the broader regional supply chain remains expensive and fragile.So, any talk about a deal of "reopening" the strait would be what markets will care about most. But then again, we have gone down this road many a time and yet there isn't any real progress to show for it come what may.As such, any exagerrated claims from US president Trump on the Strait of Hormuz "reopening" will have to be treated with caution. It may be easy for markets to get carried away on the initial headlines, but whether or not the move would be sustainable is a whole different question.If Brent crude does start holding below $100, though, the implications go well beyond oil.The immediate market read would be softer inflation pressure. That would take some heat out of the recent rise in bond yields and potentially give stocks another reason to extend their relief rally.It would also make the argument for further central-bank tightening slightly less urgent at the margin, particularly after higher energy prices became such a major part of the latest inflation scare.However, I would be careful about treating any dip below $100 as the end of the story.As long as the reality of the situation is that the Strait of Hormuz remains constrained and regional tensions remain unresolved, oil is still one headline away from another sharp reversal.It was the case in late July to early August and it could very well be the case this time around, depending on how the potential US-Iran talks play out.But at the end of the day, the real signal isn't whether Brent crude trades back below $100 to the $90s again. It is whether diplomacy can remove enough supply risk for the market to believe that sub-$100 oil can actually stick.And that remains a difficult hurdle, given how far apart Washington and Tehran still appear to be on the terms needed for any durable agreement. This article was written by Justin Low at investinglive.com.