It’s been a rough year for those in the branding business at big corporations. SEC investigations, massive product recalls and oil spills (among more traditional factors like competition and slowing sales) have taken a toll on the reputations, as well as the stock prices, of some of America’s most well-known companies.

Calculating the value of a company’s brand is as much an art as a science because it requires looking at an array of factors. The two largest brand valuations firm — BrandZ and Interbrand — come up with radically different numbers for the same companies or products. Each of the brand valuation operations give general descriptions of their methodologies, but keep many details of their calculations secret.

Using the firms’ data as a reference, 24/7 Wall St. chose 10 big-name brands operating in the U.S. that have lost substantial chunks of their brand valuations in the first half of this year. We then examined a whole host of other criteria, including the value the brand has to its parent company‘s market capitalization, the change in stock price during the first six months of the year compared to both the S&P 500 and firms in its peer group (each of these company’s stocks underperformed the broader market during the time) and the company’s earnings for the 2009 calendar year and the first quarter of 2010. Of course, another consideration was whether the company had a major negative event that made headlines. Toyota’s recalls certainly qualified, as well as BP’s massive oil spill.

Intangibles also play into 24/7 Wall St.’s calculations just as they do in other brand valuations. Numbers alone may show that BP’s brand value dropped 60% in the first half. But there’s a powerful case that BP has zero or even negative brand value because of the lasting impact the rig explosion and oil spill in the Gulf will have on the company’s financial health and reputation.

In total, the 10 companies on our list have lost well over $100 billion in brand value since Jan. 1. Here they are:

1. BP (NYSE: BP)
Brand value Jan. 1, 2010: $20 billion.
Brand value June 30, 2010: $0.
Change: -100%

BP has the distinct honor of being the only brand to lose virtually all of its value in less than a year. (The only recent comparable case is AIG.) BP’s management is reviled by nearly everyone, and its gas stations have lost plenty of customers.

The firm has put $20 billion into escrow to cover cleanup and liability costs from its Gulf oil spill, but that the amount could be far below BP’s eventual liabilities. It’s in the process of selling some assets to raise money. Chapter 11 bankruptcy protection is always a possibility however remote in most experts’ opinion. Even if BP recovers financially, its brand will suffer for years, perhaps decades. Ironically, the U.K.-based company was rated as the No. 1 oil company brand just last year by BrandZ because of its reputation for being environmentally responsible.

2. Dell (Nasdaq: DELL)
Brand value Jan. 1, 2010: $16 billion.
Brand value June 30, 2010: $9 billion.
Change: -44%.

Since founder Michael Dell returned as CEO in early 2007, Dell has been sliding. Revenue for the fiscal year ended Feb. 1, 2008 was $61.1 billion versus fiscal 2010’s $52.9 billion. Net income has been cut in half to $1.4 billion between the two periods.

#-ad_banner-#But a sales decline may be the least of the problems. In 2007, after a year-long investigation, Dell disclosed an accounting scandal aimed at inflating its financial performance. As a result, it was forced it to restate financial results for fiscal years 2003 through 2006 and for the first quarter of 2007.

Unbelievably, Dell didn’t seem to learn its lesson. In 2008, government investigators found that it had a relationship with Intel (Nasdaq: INTC) that Federal, European Union and New York State authorities claimed helped the chipmaker maintain an unfair advantage in the PC market and artificially inflated Dell’s earnings performance. Dell admitted to these transactions with Intel and recorded a $100 million liability in its first quarter of fiscal 2011 to establish a reserve for a potential settlement with the Securities & Exchange Commission. The settlement would involve a civil injunction against Dell for alleged violations of federal securities laws. Michael Dell is currently in settlement talks with the SEC.

That’s not Dell’s only legal woe. Another lawsuit, which has been ongoing for three years, claims Dell shipped as many as 12 million computers containing faulty electrical components. Some of the e-mails disclosed in the case indicate that Dell employees were aware of the problems. It’s always tough to calculate the toll suits like these take on a company’s reputation, but it’s pretty clear that Dell’s standing has sunk.

This article continues on DailyFinance.com. To continue reading about the remaining 8 companies on this list, please visit this link.