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Excessive hydrocarbons [HC] simply means something didn't finish burning. The only thing that should be burning is fuel, but a little bit of engine oil is typically consumed even in a healthy engine. If you find yourself topping off the oil level very often, then your engine consumes oil. I have no idea how much it takes to fail the emissions test. In any case, if your engine consumes more that just a tiny amount of oil, that's likely to be your problem. A good catalytic converter usually takes care of that, so the two may be related.
The other possibility is related to fuel. There's a gazillion reasons why the fuel is not being completely spent, but we can narrow it down to the most likely causes. If you have any aftermarket performance devices, consider them as a possible cause. A performance "chip" will often flunk you, as will a performance exhaust. The catalytic converter plays a huge role in emissions, and if it's damaged or simply removed or replaced with an inadequate one, that'll result in unburned fuel and flunk you again.
Also a likely and common failure point is the EGR valve, in fact, it's almost synonymous with emissions testing because it's so crucial and such a notorious offender. Dirty fuel injectors can also give you trouble, but I'd say that's probably pretty unlikely. More likely, much easier to check, and WAY cheaper to replace is the spark plugs. Spark plugs have some really unpredictable characteristics on how they affect engine performance, and even good-looking ones can be horribly faulty. Replace them with extreme prejudice.
A poor score in the hydrocarbon category doesn't necessarily equate to poor fuel economy, but each is a symptom of the other. If your economy is poor, this would explain it.
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