The increased demand for hard currencies has led to a rise in the demand for Kenyan banks.
Absa Bank Kenya leads with a margin of 10.5 percent or sh14.76, followed by Co-operative Bank of Kenya at 7.7 percent, NCBA Bank Kenya at 7.2 percent and Standard Chartered Bank Kenya at 7.1 percent.
Stanbic Bank came fifth at 6.9 percent, DTB and equity tied at 6.3 percent, followed by I&M at 5.1 percent.
KCB has a smallest spread of 3.4 percent or Sh5 on the shilling-dollar trades. The lender sold it at Sh150.95, and bought it at Sh145.95 compared to Absa's 154.98 and Sh140.22.
The Business Daily also sampled forexbureaux in Nairobi's Central Business District, finding that they offer the best deals for retail transactions at spreads of between 1.36 percent and 2.7 percent.
Satellite Forex Bureau was the cheapest, with a margin of Sh2 or 1.36 percent trading on Tuesday at Sh146 buying and Sh148 selling.
It was followed by Sterling Forex Bureau Limited at a spread of two percent or Sh3.
Wall Street Forex Bureau Dechange's spread was down at 2.7 percent - buying the greenback at Sh148 and selling it at Sh152.
The top nine Nairobi securities-exchange lenders are making billions from the increased appetite for the greenback in transactions such as imports, travel, and payments.
Absa calculated forex trading income of Sh3.76 billion in its consolidated results for the half-year ended June compared to Sh2.9 billion a year earlier, which represents a 25.9 percent increase.
StanChart's forex income almost doubled from Sh2.26 billion to Sh4.4 billion. Trading currencies is now a significant portion of banks' non-interest income, which supplements their earnings from lending to the government and the private sector.
The volatility in the forex markets has been a benefit for bankers, with the shilling decreasing, prompting businesses and individuals to begin more transactions as they stock up on hard currencies.
In the past 12 months, the local currency has depreciated 18 percent against the dollar to trade at an average of Sh147.9 to the greenback.
As of Tuesday, the spot prices on Business Daily represent what individuals and small businesses can get. However, large clients such as manufacturers and importers can negotiate better rates.
The shilling's depreciation has been influenced by the nation's reduced economic competitiveness as well as rising rates in the developed economies, causing a flow of capital from emerging and frontier markets such as Kenya.
Central banks in the US and Europe have increased interest rates to fight inflation, boosting the attractiveness of their economies.