Recent gains in online search by Qihoo 360 (NYSE: QIHU) and Sohu's (Nasdaq: SOHU) Sogou are in the headlines today, highlighting the challenges industry leader Baidu (Nasdaq: BIDU) is facing from a new rival that is quickly gaining momentum and an older rival that also appears to be gaining some traction. At the centre of the story is new data for October showing that Qihoo controlled nearly 10 per cent of the China search market , just three months after the company launched an innovative new search engine. Meantime, Sohu's Sogou search engine, launched nearly a decade ago, also posted a respectable 7.5 per cent share, as it reported its search revenue more than doubled in its latest reporting quarter. I should start off by saying that I'm just slightly skeptical of this new data, as it comes from a web analysis unit of e-commerce leader Alibaba, which seems to consider Baidu a bitter enemy even though the two companies operate in completely different areas of the Internet. But let's assume that the data is relatively reliable, which means that Qihoo and Sohu now collectively control about 15 per cent of the China search market. Baidu continued to dominate the market with 74 per cent share, while the only other significant names on the list were Google (Nasdaq: GOOG) at 5 per cent and Tencent's ( 0700.HK ) Soso at 3.5 per cent. Let's take a look at Sohu first, since the company has provided some new data on Sogou's revenue in its newly-released second quarter results. Sohu said that Sogou's revenue doubled in the second quarter to US$37 million, and was set to grow a bit more to US$40 million in the current quarter, accounting for about 14 per cent of total revenue. By comparison, Baidu's search revenue was on track to approach the US$1 billion mark in the third quarter, meaning Sogou is about 4 per cent of Baidu's size in revenue terms. That's an interesting comparison, since these October market data figures would indicate that Sohu is about 10 per cent of Baidu's size in terms of market share. Part of the difference obviously lies in the fact that Baidu, as the industry leader, can charge higher prices for its advertising. Still, Sogou's position may be overstated in this latest data, and perhaps its true market share is probably around 5-6 per cent. There's less new to say about Qihoo, since the company has yet to report its latest quarterly results. But Qihoo has been making non-stop headlines these last three months on the rapid rise of its search engine, which includes some innovative functions such as allowing users to conduct integrated searches of multiple engines and also allowing them to rate their search results. Qihoo's shares have rallied sharply on all the hype, and are now up around 50 per cent since the end of July. I admit that I like Qihoo's story, since it's nice to see someone finally challenge Baidu's years of dominance in search. I won't say Qihoo's stock is overpriced just yet, but it will have to show continued growth in the search business -- both in market share and revenue -- if it wants to keep its exciting new story alive. If it succeeds, the company could perhaps see some of the explosive growth that Baidu saw in its early days that helped to make it China's second most valuable Internet company. Bottom line : New data show that Sogou and Qihoo continue to make gains on search leader Baidu, with Qihoo potentially set to make a serious challenge against Baidu's years of dominance.