AA vs MOS: Which Is the Better Buy in 2026?

Same yardstick, side by side (as of October 2026). Valuation lined up like this is most meaningful for two names in the same corner of the market, which these are. Figures are approximate; verify before investing.

Reading it: AA is the cheaper of the two on forward earnings, but cheaper is not the same as better. Pair the valuation with growth (how far the forward P/E sits below the trailing P/E) and risk (beta) before you decide.

The metrics above tell you which is the marginally better business. The bigger risk for most people is not picking the slightly worse stock, it is over-concentrating. AA and MOS share themes, so owning both, or adding either to what you already hold, can quietly push a large share of your portfolio into one bet.

This is the part a generic comparison page cannot answer, because it depends on what you own. Connect your brokerage and Walnut shows your real, combined AA and MOS exposure, flags overlap with your existing positions, and tells you if adding one would tip you past a concentration you are comfortable with, read-only by default, with your login staying at your broker. Walnut is not an investment adviser.

Alcoa Corporation is one of the world's largest upstream aluminum companies, running the full chain from bauxite mining to alumina refining to aluminum smelting. It reports in two segments: Alumina (about 2.5 million metric tons produced in Q3 2026) and Aluminum (about 649,000 metric tons in the same quarter). Because it sells raw and semi-finished metal into global markets, Alcoa is a price-taker: its revenue and margins are driven mainly by the London Metal Exchange aluminum price and the alumina price index, plus its own energy and raw-material costs. That makes it different from downstream fabricators like Arconic that sell finished, engineered products at steadier margins.

Full AA guide

The Mosaic Company is a leading global producer and marketer of concentrated phosphate and potash, the two primary crop nutrients it mines, processes, and distributes to farmers and dealers worldwide. Its business runs across three reporting segments: Phosphates (finished phosphate fertilizers plus premium products like MicroEssentials), Potash (potassium fertilizer from mines in Saskatchewan, New Mexico, and elsewhere), and Mosaic Fertilizantes, a large Brazil-based production and distribution arm that now drives roughly a third of the company's business. Mosaic sells into agriculture, where nutrient demand is tied to planted acreage, crop prices, and farmer economics.

Full MOS guide

Both fit overlapping themes, but they are not interchangeable. The useful comparison is which set of drivers and risks you want exposure to.

• AA drivers: Aluminum price and supply gap; Restarts and higher volumes.
• MOS drivers: Global crop-nutrient demand; Potash and Esterhazy productivity.

A faster-growing, richer-valued name usually swings harder, so it suits a longer horizon and a higher tolerance for volatility; a steadier, more cash-generative business suits a more conservative or income-minded investor. The honest test is which set of risks you could hold through a drawdown: The dominant risk is commodity price cyclicality: with revenue tied to aluminum and alumina indices, a global slowdown or a swing in Chinese supply can compress earnings quickly, and the stock's roughly 23% decline in 2026 despite higher profits shows how fast sentiment can turn. For MOS, mosaic is a cyclical commodity producer, so its earnings can swing dramatically with potash and phosphate prices and are exposed to sharp input-cost inflation in sulfur, ammonia, and natural gas.

Growth-minded investors who believe the theme has years to run tend to accept the richer multiple for more upside; value-minded investors lean toward the cheaper forward earnings and steadier profile. Pick AA if you believe its drivers more; MOS if you believe its. Many investors hold both, but since they share themes, that is a concentrated bet, not diversification. Decide deliberately and check overlap. For the full detail, see the AA and MOS guides.

AA. Figures are approximate and tied to the asOf date; verify live numbers before acting. For a cyclical producer, a forward P/E under 8x can be a trap because it reflects strong-cycle earnings that consensus already expects to fall about 18% in 2027, so the multiple says more about where aluminum prices sit than about the company. Analyst targets around $60 imply upside from the mid-October price, but that view is a bet on the commodity as much as on Alcoa.

MOS. Mosaic trades at about ~0.5x sales and ~0.5x book value, levels typical of a commodity producer near a cyclical low, and the trailing P/E is not meaningful because of the ~$639 million trailing loss. The ~12x forward multiple assumes earnings recover toward ~$1.52 per share in 2027. The ~$26 average analyst target sits well above the October 16 close, but several targets were cut in October 2026 as input-cost pressure persisted.

Headline figures (approximate, October 2026): AA shows revenue (ttm) ~$14.3 billion (Q3 2026 ~$3.70 billion, up ~24% year over year), net income (ttm) ~$1.5 billion (Q3 2026 ~$483 million); net margin ~11%, adjusted eps (q3 2026) ~$1.82 vs ~$1.51 consensus; trailing EPS ~$4.81, operating margin ~16% (gross margin ~23%); MOS shows revenue (ttm) ~$12.25 billion, q2 2026 revenue ~$2.82 billion (down ~6% YoY), net income (ttm) ~$639 million net loss, forward p/e ~12x (trailing not meaningful).

AA and MOS are related but distinct: same themes, different businesses and risks. Neither wins in the abstract; the right pick is whichever thesis you actually believe, sized so you are not over-concentrated in one theme. Walnut can show your combined AA and MOS exposure against your real portfolio. It is not an investment adviser.