Best estimates from the Gumshoe are that roughly 1% of my readers will be online this weekend and actively keeping up with the exciting Gumshoe news … so while I love you all, and most especially adore the faithful readers who sit in their seats at Gumshoe University even on Labor Day weekend, I must admit to a certain reluctance to throw my all into a new sleuthing job that no one will get around to reading.

But I have noticed a huge surge of interest in geothermal stocks again, on the back of another big email campaign using the “slow volcano” term — this is from the Energy and Scarcity Investor newsletter from Byron King at Agora, and it is among several ad campaigns based on geothermal stocks that we’ve seen here in the past year. So today, a list of all those firms that we’ve looked at or written about:

Most recently, we’ve seen crop up a few times the ad touting a company that is supposedly making Saudi Arabia quake in its boots — this ad is from the Oxford Club, and it touts Raser Technologies /a> as the leader of the “post oil” future. That stock has been pretty bumpy, it was around $10 when this campaign lifted off, and the ad ran for much of the Summer, eventually enjoying some spikes up to over $11, but the shares are well off those highs now.

A few months before that, Raser Technologies was also being hyped by Trinity Research, for much the same reasons.

The original Slow Volcano Power teaser ad, though it’s running hot and heavy now, actually started appearing last November (the main stock was and is Western Geothermal, and there are also a slew of other stocks mentioned) — from what I can see, this ad hasn’t changed much in nine months.

And Greg Guenthner at Bulletin Board Elite was touting Western Geothermal well before that.

Before that, it was the teaser for US Geothermal by Green Chip Stocks — that pick was the strongest of the Geothermal touts, and remains a solid performer even though it’s way, way off its highs of last Fall (it also got a listing on an exchange later on and no longer trades over the counter, the ticker is now HTM if you’re looking for it).

So far, the only consistent thing about these stocks is that they’re all down pretty significantly over the last six months to a year, or are otherwise well off their highs. Those highs for geothermal stocks seem to be driven by media attention and these email ad campaigns, and probably also by natural gas and oil prices to some degree. Most of the firms are at a very early stage in developing geothermal plants or technology, those plants are big, slow-moving, capital-intensive projects, and they don’t have much cash flow to show for their efforts just yet (the existing geothermal plants in the US are largely owned by big utilities, and have been around for years).

I love the idea of geothermal energy, but the barriers to really wide adoption seem pretty high, unless Raser’s most optimistic projections are realized and lower-temperature geothermal generation becomes really feasible (if you need a real geologic hotspot for geothermal generation, like the Geysers or like Iceland, there aren’t all that many in the US). That doesn’t mean that these companies can’t make any money or be successful, but they’re not making much just yet.