Serious Money: What are the similarities between the Irish property market and oil prices? Both assets have risen further and for longer than anybody expected and both now have bubble element to their valuations.

Serious Money has previously backed both oil and Irish real estate to rise in price but the time has come to declare enough is enough.

While the presence of financial bubbles is fiendishly difficult to prove - until they burst that is - there is enough circumstantial evidence to suggest that good, old-fashioned speculation has taken prices in both markets to levels far in excess of what is likely to prove sustainable.

The case for believing that house prices cannot rise much further, and might even fall, is well rehearsed. Consumer debt levels have reached dangerous levels, house price to income ratios are off the charts and one or two high-profile land deals make little financial sense to the outside observer.

All of this could have been said about the Australian, UK, US and Irish property markets at various points in the recent past. Both the UK and Australian markets have decisively rolled over and there are one or two straws in the wind suggesting the US is about to do the same - hot spots like Florida and Southern California are, anecdotally at least, coming off the boil.

If international markets set the trend and we have been a not insignificant part of what some have called the global price bubble, then Irish property prices are due for a stumble.

The debate over energy prices is also well known. Demand for crude oil is soaring, driven in part by China and India but also by the voracious appetite of the US. Prices are rising mostly because of supply failing to keep up with demand. And most - but by no means all - of the available data are consistent with the idea that the latest oil shock is down to demand rather than supply, the opposite of Opec dominated oil shocks of the 1970s.

A big clue to potential existence of a bubble is the observed set of reasons given by oil experts for the push in oil prices from $50 (€41) per barrel to their recent peaks of $70. During this period we were told that an imminent fall in the house of Saud was combining with the fundamental supply/demand imbalance already observed.

Tightness in the crude market is also combining, we are told, with lack of oil-refining capacity in Europe and the US to push up petrol and other refined prices.

Now, when the house of Saud didn't fall, oil prices stayed high. More importantly, all that stuff about ever tighter supply/demand imbalances turns out, on close inspection, to be mostly nonsense, at least for crude oil. As a matter of fact, US oil stocks, for example, have been steadily rising all year and currently stand at multi-year highs. More generally, if economic growth is the driver of high oil prices, there is no evidence to suggest that the global economy suddenly took off when oil reached $50 per barrel, sufficient to drive the price up another 40 per cent.

Think about those arguments about refining. If there is a shortage of refining capacity there is no logical reason why crude oil prices should rise. There is no problem for the refiners getting their hands on crude oil, it is their lack of capacity to turn the stuff into petrol that is the problem. The price of refined products should be rising relative to crude oil prices: refiners' margins should be expanding (another reason to buy certain types of oil shares, such as the Spanish company Repsol).

When the reasons for higher asset prices don't stand up to scrutiny we begin to sniff a problem. But this is not to say that a crash in either oil or property prices is likely. Markets have a nasty habit of trying to forecast prices that will either soar or slump, but there are plenty of reasons to think that both oil and real estate prices, once they make an initial downward adjustment, should then move sideways (and stay relatively high into the medium term). If oil prices do fall back towards $50 per barrel, markets being what they are will probably mark down the share prices of oil companies, possibly quite aggressively. This will be a buying opportunity: share prices of oil companies are still cheap, in my view, even if oil falls by $15-$20.

The resilience of equity markets in the face of ever-increasing oil prices does tell us something about the underlying robustness of economies and corporate profits. But a tipping point for growth must come somewhere. Growth is not immune to the oil price; there must come a point where growth is threatened.

I don't know whether that is at $70 or $100 for a barrel of oil but I suspect it's sooner rather than later. But if the oil price does slide in the way that I think it might, this will come as a significant relief for stock markets and will give another significant boost to cyclical sectors and stocks.

Oil and property are related in another obvious way. If I am wrong about the oil price and it heads on for $100 per barrel, property - and not just of the Irish variety - will not go up much further.

Indeed, many assets of all kinds will be hit hard by the implications for growth. Much depends on the current oil price proving to be something of a bubble.

Chris Johns is an investment strategist with Collins Stewart. All opinions are personal