Few commodities are ruled more by emotion than common sense at times than gold and silver.

Both precious metals have had quite the topsy-turvy performance since the beginning of 2016. Part of the blame for an increase in volatility associated with precious metals can be traced to conflicting and often changing short-term data. Questions such as "Will the Fed raise rates or back off and wait?" continue to dominate the headlines. Uncertainties over Brexit, the French elections, and an inexperienced Donald Trump as president have also given way to short-term rallies and sell-offs in precious metals.

A gold and silver bar stacked next to one another.

Image source: Getty Images.

Take note: The gold-to-silver ratio is soaring

As of the closing bell on Monday, May 8, something new caught my attention: The gold-to-silver ratio is beginning to creep significantly higher.

Simply put, the gold-to-silver ratio describes how many ounces of silver it would take to equal one ounce of gold. Throughout the 20th century, this average gold-to-silver ratio was 47-to-1, so this often serves as a baseline that precious metal enthusiasts and gold and silver mining stock investors utilize in deciding where to put their money. If this ratio falls notably below 47-to-1, gold is assumed to be the more attractive investment opportunity of the two metals. Meanwhile, if this ratio balloons well above its 20th century average, silver may offer the better return potential.

As of Monday's closing values for gold ($1,226 per ounce) and silver ($16.20 per ounce), the gold-to-silver ratio has jumped to 75.7-to-1. Over the past 17 trading sessions, gold is off a hair more than 5%, while silver has shed almost 13% of its value.

Understandably, solely placing your hopes on the back of the gold-to-silver ratio isn't a wise idea. Supply and demand still matter, as does the outlook for global growth and the Federal Reserve's monetary policy. But, as we've recently examined, the outlook for both precious metals remains fairly positive, despite a few setbacks.

If silver outperforms, these are the mining stocks to consider buying

With that being said, if silver outperforms in the months and years to come in relation to gold, here are the three stocks you should consider adding to your portfolio.

A silver bar on a dark background.

Image source: Getty Images.

1. Wheaton Precious Metals

Wheaton Precious Metals (NYSE:SLW) (formerly Silver Wheaton) isn't your traditional mining company, but that in no way makes it less attractive as an investment.

Wheaton Precious Metals' business model involves providing large sums of capital to mining companies looking to develop or expand a mine. In return, it receives a percentage of production well below market price for an extended period of time. It essentially means that aside from the expense of handing over a large sum of money to its partners, it has minimal overhead expenses. It also means the price of silver has a more immediate margin impact on Wheaton Precious Metals than any other silver stock, even though the other two silver miners below derive a higher percentage of their revenue from silver than Wheaton Precious Metals.

According to the company's fourth-quarter and full-year report released in March, where it delivered record revenue and sales volume, its average silver cash costs were $4.42 per ounce. This represented a cash operating margin of $12.54 per silver ounce based on the average selling price of $16.96 per ounce in 2016.

Though Wheaton Precious Metals is at the mercy of its producers at times (e.g., the shutdown of the San Dimas mine for two months will certainly hinder its silver production in 2017), its low-cost and high-margin structure make it the perfect stock to take advantage if spot silver outperforms gold.

An underground excavator in a silver mine.

Image source: Getty Images.

2. First Majestic Silver

If you're looking for the closest thing to a pure play in the silver mining industry, then First Majestic Silver (NYSE:AG) is your company to consider buying.

Many silver miners have shifted their production portfolio away from a sole reliance on silver. A good example being Silver Standard Resources (NASDAQ:SSRI) which, following its acquisition of gold miner Claude Resources and the stoppage of silver production at its San Miguel open mine pit, is a company that's now more than 80% reliant on gold for its revenue generation. It's no wonder that Silver Standard Resources will soon be changing its name to SSR Mining to reflect this production shift.

Meanwhile, First Majestic Silver nets around 70% of its revenue from the sale of silver at its six producing mines, at least according to production estimates in 2017 from Bank of Montreal. Ongoing expansion at La Encantada, Del Toro, and La Guitarra should fuel organic existing mine growth, while Plomosas and La Luz could be in the commercial production phase within the next two to four years. Both have the potential to deliver roughly 2 million ounces of silver annually. After generating 11.9 million ounces of silver in 2016, First Majestic is aiming for 20 million ounces by the end of the decade. 

Once again, if physical silver outperforms gold, then First Majestic Silver, which is more dependent than any other publicly traded mining company on silver, should do well.

Three dump trucks driving in an open pit mine.

Image source: Getty Images.

3. Endeavour Silver

The third silver mining stock to add to consideration is Endeavour Silver (NYSE:EXK), which has mining assets in both North and South America. Based on estimates for 2017 revenue generation from Bank of Montreal, Endeavour should generate somewhere between 60% and 65% of its sales from silver, putting it behind only First Majestic Silver in terms of sales reliance.

However, unlike Wheaton Precious Metals and First Majestic, Endeavour Silver has seen production head in reverse recently. Management has been very cautious given volatile precious metal pricing, and it's resulted in substantially lower costs but also reduced output. Silver and gold production fell a respective 29% and 27% during the first quarter.

Yet, there's hope on the horizon. Endeavour recently gave the green light to move forward with the El Compas mine, which would become its fourth producing mine, and it appears on track to soon approve construction for Terronera, which would be its fifth producing mine. A sixth potential mine, Parral, waits in the wings and could be approved to begin construction within the next two years. Based on estimates from Endeavour's May 2017 corporate presentation, El Compas' payback period is a mere 2.1 years, while Terronera would have a payback period of just 4.3 years.

If Endeavour Silver can maintain its exceptionally low costs while also working on these aforementioned three new projects, and silver outperforms gold, look out above.

Sean Williams owns shares of Silver Standard Resources and Silver Wheaton. The Motley Fool owns shares of Silver Wheaton. The Motley Fool has a disclosure policy.